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Assessment of Iodine
Deficiency Disorders and Monitoring their Elimination : A guide for programme
managers, Second Edition. ICCIDD/UNCF/ WHO, 2001
Introduction
About this manual
The importance of iodine
deficiency disorders (IDD)
Iodine
deficiency, through its effects on the developing brain, has condemned millions
of people to a life of few prospectus
and continued
underdevelopment. On a
worldwide basis, iodine deficiency is the
single most important preventable cause
of brain damage.
People living
in areas affected by severe IDD
may have an intelligence quotient (IQ) of up to about
13.5 points below that of those from comparable communities in areas
where there is no iodine deficiency (1). This mental deficiency has an immediate effect on child learning capacity,
women's health, the quality of life of communities, and economic productivity.
On
the other hand, IDD are among the easiest and cheapest of all disorders
to prevent. The addition of a
small, constant amount of iodine to the salt that people consume every
day is all that
is needed.
The elimination of IDD is a critical
development issue, and should be
given the highest priority by governments and international agencies.
Recognizing the importance of preventing IDD, the World
Health Assembly adopted in
1991 the goal
of eliminating iodine deficiency as a public health problem
by the year 2000. In 1990, the world's leaders had endorsed this goal when
they met at the World
Since
1990, there has been tremendous progress in increasing the amount of salt which is adequately iodized. As a
result, many countries are now on the threshold of acieving IDD elimination.
In those countries, the emphasis will shift to ensuring that the achievements are sustained for all time.
Objectives of this manual
Progress
towards the elimination of IDD can only be
demonstrated if it is
measured. This requires the selection of
appropriate indicators of both process and impact (what is measured and
why).
Techniques
are then needed to measure these indicators (how they are
measured). These techniques
have to be
applied using suitable
epidemiological methods (who, where, and when).
Finally,
the results have to be presented in a digestible format, comparable with those
from other regions or countries.
Specifically, the objectives of this manual are to describe:
* the indicators used in assessing the baseline
severity of IDD, and in monitoring and
evaluating salt iodization and its
impact on the target populations;
* how to use and apply these indicators in
practice;
* how to assess whether iodine deficiency has
been successfully eliminated; and
* how
to judge whether achievements can
be sustained and maintained for the decades to come.
Target
audiance
This
book is aimed primarily at IDD programme managers and others in government
who are involved in the implementation of IDD
control programms. It is also aimed at
the salt industry and all others
involved in IDD elimination.
Origins of this book
This is a
revised version of the original document,
which was entitled "indicators for assessing Iodine Deficiency
Disorders and their control
through salt iodization" (2).
That document was produced
following a consultation held in
Since
the consultation, a considerable body of new information on the identification, prevention
and control of IDD
has been generated, and the
public health focus regarding this significant problem has shifted to emphasize the importance
of the
process indicators. To continue the battle against IDD into
the new millennium, these
new concepts have
been incorporated into
international guidelines
for assessing and eliminating
these disorders.
The Consultation on which this book is based was
held in
Definitions
Iodine Deficiency Disorders refer to all of the ill-effects
of iodine deficiency in a
population, that can be prevented
by ensuring that the population
has an adequate intake of iodine.
For further details, see section 2.
An indicator is used to help describe a
situation that exists, and
can be used to track changes in
the situation over
time. Indicators are
usually quantitative (i.e.
measurable in some way), but they may also be qualitative.
Monitoring is
the process of collecting,
and analysing on a
regular basis, information about a
programme for the purpose of
identifying problems, such
as non-compliance, and
taking corrective action so as to fulfil stated objectives.
Evaluation is
a process that
attempts to determine
as systematically and objectively
as possible the
relevance, effectiveness, and impact of activities in the light of
their objectives (3).
Monitoring and evaluating IDD control programmes
Monitoring
of any health intervention is essential, to check that it is
functioning as planned and
to provide the
information needed to take
corrective action if
necessary. In additon, periodic evalution of health programmes is necessary to
ensure that overall goals and objectives are being met.
Salt iodizatio programmes, like any other
health interventions, therefore require
an effective system
for monitoring and evaluation. The challenge is to apply the IDD
indicators using valid and reliable
methods while keeping costs to a minimum.
To this end, it is essential to
formulate clearly the questions to which answers are needed, since the methods used to
gather data may be very different. Important questions that will need to be answered include:
* Is all the salt that is being produced or
imported iodized to the country's
requirements?
* Is the salt adequately iodized?
* Is adequately iodized salt reaching the
target population?
* What impact is salt iodization having on the
iodine status of the population?
* Have IDD been eliminated as a public health
problem?
In some countries there is still inadequate
information on IDD, and programmes have
not yet been implemented. Here the
questions may be:
* Is there a significant IDD problem?
* What is the prevalence of IDD in a given
population?
* Where does the salt come from that people
buy?
Answering these
questions requires different
approaches to gathering
data. It is therefore very important to
be quite clear about the purpose of a particular survey.
Indicators described in this manual
This manual describes the various indicators which
are used
in monitoring and evaluating IDD control programmes. The indicators are divided into three main
groups:
* Indicators to monitor and evaluate the salt
iodization process (process indicators)
These indicators involve salt iodine content
at the
production site, point of packaging, wholesale and retail
levels, and in households.
* Indicators to assess baseline IDD status and
to monitor and evaluate
the impact of salt iodization on the target population (impact indicators)
Once a
salt iodication programme
has been initiated,
the prinicipal impact indicator
recommended involves urinary iodine
levels. Changes in
goitre prevalence lag behing changes
in iodine status and therefore cannot be relied upon
to reflect accurately current
iodine intake, although they may be useful
in following trends.
Goitre
assessment, by palpation or by ultrasound, shoulf remain a component of surveys to establish the baseline severity
of IDD.
Neonatal thyroid stimulating hormone (TSH) levels may also play a role
here if a country already has in place a screening programme for
hypothyroidism.
* Indicators
to assess whether iodine
deficiency has been successfully eliminated and to judge
whether achievements can be sustained
and maintained for the decades to come
(sustainability indicators)
This involves a combination of median urinary
iodine levels in the target population, availability of
adequately iodized salt at the household
level, and a set of programmatic indicators
which are regarded as evidence of sustainability.
IDD and their
control, and global
progress in their elimination
The Iodine Deficiency Disorders
Recommended iodine intake
WHO,
UNICEF, and ICCIDD (4) recommended that the daily intake of iodine should be as follows:
* 90 ug for preschool children (0 to 59
months);
* 120 ug for school children (6 to 12 years);
* 150 ug for adults (above 12 years); and
* 200 ug for pregnant and lactating women.
The Iodine Deficiency Disorders
Iodine deficiency
occurs when iodine
intake falls below recommended levels.
It is a natural ecological phenomenon
that occurs in many
parts of the world. The
erosion of soils
in riverine areas due to
loss of vegetation from
clearing for agricultural production,
overgrazing by livestock
and tree-cutting for firewood, results in a continued and
increasing loss of iodine from the soil.
Groundwater and foods grown locally in
these areas lack iodine.
When iodine intake falls below recommended
levels, the thyroid may
no longer be
able to synthesize sufficient
amounts of thyroid hormone. The resulting low level of thyroid hormones in the
blood (hypothyroidism) is the principal
factor responsible for the damage
done to the developing brain and the other harmful effects known
collectively as the Iodine
Deficiency Disorders (5). The
adoption of this term
emphasized that the
problem extended far beyond
simply goitre and cretinism (see Table 1).
Table 1: The spectrum of the Iodine Deficiency
Disorders (IDD)
FETUS Abortions
Stillbirths
Congenital
anomalies
Increased
perinatal mortality
Increased
infant mortality
Neurological
cretinism:
mental
deficiency, deaf mutism,
spastic
Diplegia squint
Myxoedematous
cretinism:
mental
deficiency, dwarfism, hypothyroidism
Psychomotor
defects
NEONATE Neonatal
hypothyroidism
CHILD
& Retarded mental and physical
development
ADOLESCENT
ADULT Goitre
and its complications
Iodine-included
hyperthyroidism (IIH)
ALL
AGES Goitre
Hypothyroidism
Impaired
mental function
Increased
susceptibility to nuclear radiation
The most
critical period is
from the second
trimester of pregnancy to the
third year after birth (6,7). Normal
levels of thyroid hormones
are required for optimal
development of the brain.
In areas of iodine
deficiency, where thyroid
hormone levels are low, brain development is impaired.
In
its most extreme form, this results in cretinism, but of much greater
public health importance are the more subtle degrees of brain
damage and reduced cognitive
capacity which affect
the entire population. As a
result, the mental ability of ostensibly normal
children and adults living in areas of iodine deficiency is reduced compared to what it
would otherwise be.
Thus, the
potential of a whole community is reduced by
iodine deficiency. There is
little chance of
achievement, and
underdevelopment is perpetuated. Indeed, everybody may seem to
be slow
and rather sleepy. The quality of
life is
poor, and ambition blunted.
The
community becomes trapped in a self-perpetuating cycle. Even the
domestic animals, such as the
village dogs, are affected.
Livestock productivity is also dramatically reduced (8).
Identification of the occurrence of IDD
In the
past, the likely occurrence of IDD is
given region was regarded as
being signaled by
certain geographical
characteristics. These include mountain ranges
and alluvial plains, particularly
at high attitude
and at considerable distance from the sea.
This occurrence is confirmed by
a high prevalence of goitre in
the resident population.
However,
the greater availability of urinary iodine estimation and other methods for assessing iodine deficiency has
demonstrated that IDD can
and do occur in many areas where
none of these
conditions are met. Indeed, significant iodine deficiency
has been found:
* where
the prevalence of goitre, as based
on palpation, is normal;
* in coastal areas;
* in large cities;
* in highly developed countries; and
* where IDD have been considered to have been
eliminated, either by prophylactic programmes or general dietary changes.
In recognition
of the much
wider occurrence of
IDD than previously thought,
certain countries have come to
regard the whole country as being
at risk of iodine deficiency and therefore the entire population as a target of
IDD control by iodized salt. The need
for continued vigilance is
underlined, as is the
importance of all countries carrying out periodic urinary iodine
surveys.
Correction of iodine deficiency
An iodine deficient environment requires the
continued addition of iodine, which is
most conveniently and cheaply achieved by the addition of iodine to the salt supply. Most humans eat salt in roughly the same amount each day.
A decrease in salt intake can be readily met
by increasing the iodine content. Where a significant amount of processed
food is consumed, it is important that
the salt used by the food industry is
preparing such food - as well as the salt used in the home - is iodized.
Universal
salt iodization, which ensures that all salt for human and animal consumption is adequately
iodized, has been remarkably successful
in many countries.
At this stage,
however, sustainability of this successful coorection of iodine
deficiency becomes the challenge, as iodine deficiency may recur at any time
(9).
In
some regions, iodization of salt may not be a practical option for the
sustainable elimination of IDD, at least in the
short term. This is particularly
likely to be the case in remote areas where
communications are poor or where there are numerous
very small-scale salt producers.
In
such areas, other options for correction of IDD may have to be considered such
as:
* administration of iodized oil capsules every
6-18 months (10);
* direct
administration of iodine solutions, such
as Lugol's iodine, at regular
intervals (once a month is sufficient); or
* iodization
of water supplies by direct
addition of iodine solution or via a special delivery
mechanism.
There is much evidence that correction of iodine
deficiency has been followed by a
"coming to life" of a community suffering from the effects
on the brain
of hypothyroidism due
to iodine deficiency. Such
as increase in vitality is responsible
for improved learning by school
children, improved work performance
of adults, and
a better quality
of life. The
economic significance of the prevention of iodine deficiency
disorders needs to be clearly understood (11).
Education about these basic facts has to be
repeated, with the inevitable changes over time in Ministries of
Health and among technocrats and
salt producers. Otherwise,
a successful programme will
lapse, as has occurred in a number of countries.
Universal salt iodization
In
nearly all countries where iodine deficiency occurs, it is now well recognized
that the most effective way
to achieve the virtual
elimination of IDD is through universal salt iodization (USI).
USI involves
the iodization of all human
and livestock salt, including salt used in the food
industry. Adequate iodization of
all salt will deliver iodine in the
required quantities to the population on a continuous and
self-sustaining basis.
National salt iodization programmes are now applied
worldwide, and have followed a
common pattern of evolution, which
includes the following phases.
* Decision phase: the purposes of this phase are to enable
a decision on universal
salt iodization supported by
industry mobilization, standards and regulation, and to prepare a plan
for
implementation.
* Implementation phase: the phase ensures infrastructure for iodization and
packaging of all human and livestock
salt, and supports that
infrastructure with quality
assurance, communications, regulation, and enforcement.
* Consolidation phase: once the goal of universal iodization is
achieved, it needs to be sustained
through ongoing process and impact monitoring and periodic
evaluation; the latter may include international multidisciplinary teams.
A successful
salt iodization programme at
the national level depends upon the implementation of a
set of activities by various sectors:
* government
ministries (legislation and
justice, health, industry,
agriculture, education, communication, and finance);
* salt
procedures, salt importers
and distributions, food manufacturers;
* concerned civic groups; and
* nutrition, food and medicial scientists, and
other key opinion makers.
Opening
the channels of communication and maintaining
commitment and cooperation across
these various groups is
perhpas the greatest challenge
to reaching the IDD elimination
goal and sustaining it forever.
Salt
producers and distributios are instrumental in ensuring that IDD is
eliminated. Protecting consumers
requires that a framework
be established to
ensure the distributions of adequately packaged, labelled, iodized
salt. The setting of this framework is the main responsibility of the government.
Ensuring a demand for the product and
understanding the reason for
insisting upon only iodized salt is a shared responsibility of the private salt marketing system, the
government, and civic society. The establishment and maintenance of such
an alliance and all of the associated programme elements will
determine the success and sustainability
of the programme.
A
guideline has been developed as a useful tool to aid the review of all aspects
of a comprehensive salt iodization programme (12). This
guideline, however, will need to be modified according
to the particular country situation.
Sustainability
The remarkable
progress of universal salt iodization
in the current decade
poses the issue
of sustainability. Indeed, sustainability is absolutely
critical.
IDD
cannot be eradicated in one great global effort like smallpox and, hopefully
poliomyelitis. Smallpox and poliomyelitis
are infectious diseases with only
one host - man. Once eliminated,
they
cannot come back.
By contrast, IDD is a nutritional deficiency
that is
primarily the result of
deficiency of iodine in soil and water.
IDD can therefore return at any time after their elimination
if control programmes
fail. Indeed, there
is evidence that
iodine deficiency is returning
to some countries where it had
been eliminated in the past (13).
IDD can
only be elimination
once and for
all if control programmes are constantly maintained.
In other words, iodine must be provided permanently to populations living in
iodine deficient environments or where no iodized food is imported.
Whether countries
are deemed IDD-free, close
to the
goal of universal salt
iodization, or still have some distance to go, the vital message
is clear. All efforts must be
maintained, and programmes must
be sustained. Where they are weak, they
must be strengthened.
Three major
components are required
to consolidate the elimination of IDD and to sustain it
permanently:
* Political support
* Administrative arrangements
* Assessment and monitoring system
Political support
This refers primarily to support at
govrnmental level, through the
Minister of Health and the
executive group of
government (Cabinet or
equivalent). Political support for
the elimination of IDD depends on community awareness and
understanding of the problem.
Without
this community awareness, politicians are unlikely either to be aware or willing to act. Political support is
essential for the passage of laws or regulations on salt iodization
through the legislature.
Administrative arrangements
The National
Body responsible for the
management of the
IDD control programme should
operate with a process model. A useful
example of such a process model is known
as the "wheel" (Figure 1,
following page).
This model shows the social process involved in
a national IDD control
programme. The successful
achievement of this process requires the establishment of a
national IDD control commission,
with full political and legislative
authority to carry it out.
This model, which is described in detail on the opposite page, is being
followed in a number of countries.
The social process involves six components, clockwise in the hub of the wheel.
1. Assessment of the situation requires baseline
IDD prevalence surveys, including measurement of urinary iodine
levels and an analysis of the salt situation.
2. Dissemination of findings implies communication to
health professionals and the public, so that there is full understanding
of the IDD problem and the potential benefits of elimination.
3. Development of a plan of action includes
the establishment of an intersectoral task force on IDD and the
formulation of a strategy documet on achieving the
elimination of IDD.
4. Achieving
political will requires intensive
education and lobbying of politicians
and other opinion leaders.
5. Implementation needs
the full involvement
of the salt industry. Special measures, such as negotiations
for monitoring and quality control of imported iodized salt,
will be required. It
will also be necessary to ensure that iodized salt
delivery systems reach all
affected populations, including the
neediest. In addition,
the establishment of
cooperatives for small producers, or restructuring to larger
units of production, may be needed. Implementation
will require training at all levels in management, salt
technology, laboratory methods,
and communication.
6. Monitoring and evaluation requires the
establishment of an efficient
system for the collection of relevant scientific data on salt iodine content and urinary
iodine levels.
The multidisciplinary orientation
required for a
successful programme poses special
difficulties in implementation. Experience indicates that particular problems
often arise between
health
professionals and the salt industry - with their different professional orientations.
There is need for mutual education about the health and development problems of IDD,
and about the problems encountered
by the salt industry
in the continued production of
high quality iodized
salt. Such team work
is required for sustainability to be achieved.
The additional
cost of iodine fortification in the
process of salt production
(less than 5 US cents per person
per year in 1999) should eventually be borne by an
educated community. This will greatly
assist sustainability.
Assessment and monitoring system
It is
necessary to provide adequate dietary iodine to prevent
brain damage in the fetus and in the young infant when the brain is
growing rapidly. Whether or not a national
programme is providing an adequate amount of iodine to the target population is
reliably assessed by reference to measurements of salt iodine (at the factor, retail, and household
levels) and urinary iodine (measured in
casual samples from school children or
households). Additional contributive measurements are estimation of
thyroid size and blood tests.
Measurements of salt
and urinary iodine thereby provide
the essential elements for
monitoring whether IDD
is being successfully
eliminated. These measurements must be
carried out regularly, according to the
procedures described in this manual.
Accordingly,
appropriate measures can be taken, if necessary, to ensure
the normal range
of intake of
iodine. All these procedures require
internal and external
quality control in order to ensure reliability of the data
collected.
In order to be effective, the surveillance system needs:
* Laboratories, for
measurement of salt iodine and
urinary iodine, which are
available at the country and
regional levels with some
support from international laboratories
for quality control: regional
reference laboratories are
important for sample exchange to
ensure external quality control; and
* production
quality assurance charts and
database at the country
level, for recording
the results of
the regular monitoring procedures
- particularly for salt
iodine, urinary iodine, thyroid
size and, when available, neonatal TSH.
These facilities must be backed up by the provision
of adequate resources. Money, trained manpower, eqipment, and
materials are also required to support the implementation
of salt
iodization and the establishment of monitoring systems.
Global progress in the elimination of IDD
In 1999, WHO estimated that of its 191 Member
States, 130 had a significant IDD problem.
A total of approximately 740 million people were
affected by goitre - 13%
of the world's
total
population
(14). Given that goitre represents the
tip of the IDD iceberg (5), it is likely
that a much greater proportion of the
population suffers from IDD and, in particular, from some degree of mental retardation.
While the struggle to conquer IDD started in the
early years of the twentieth
century, the last decades has seen
the greatest progress. That progress has been particularly rapid in
In spite of the progress, however, the estimated
number of the total
affected population at the global
level has not changed substantially compared with the figure previously published
in 1993 (15). The
reason lies in the fact
that in 1993
the magnitude of the problem had been underestimated because some of the information was not yet available.
Table 2: Current magnitude of IDD by goitre
by WHO Region (1999)
|
WHO Region |
Population in millions* |
Population affected by
goiter in millions |
% of the Region |
|
|
|
|
|
|
|
612 |
124 |
20% |
|
The |
788 |
39 |
5% |
|
|
1477 |
172 |
12% |
|
|
869 |
130 |
15% |
|
|
473 |
152 |
32% |
|
Western Pacific |
1639 |
124 |
8% |
|
Total |
5858 |
741 |
13% |
Source:
WHO Global IDD Database (to be published).*Based on UN Population Division
estimates, 1997.
In
1999, WHO in collaboration with UNICEF and ICCIDD reviewed the IDD global
situation (14). Of the 130
countries with IDD, 98 (75%)
now have legislation on salt
iodization in place, and a further 12 have it in draft form.
Following the
promulgation of legislation
on salt, and
the sensitization of the salt
industry, there has been an enormous increase in the consumption of
iodized salt. The latest data for each
of WHO's Regions are summarized in Table 3.
Table 3:
Current status of salt iodization coverage
by WHO Region (1999)
|
WHO Region |
Percentage of households with access to iodized
salt* |
|
|
63% |
|
The |
90% |
|
|
70% |
|
|
27% |
|
|
66% |
|
Western Pacific |
76% |
|
Overall |
68% |
Source: adapted
from WHO, UNICEF, ICCIDD.
Progress towards elimination of
iodine deficiency disorders (14).
*Total
population of each country multiplied by the percentage of households with access to iodized salt. Numbers
then totalled for each
Region and divided by the
total population of
that
Region.
This report
(14) emphasizes the importance
of monitoring for ensuring
the sustainability of IDD
control programmes. The latest
data from the same report, concerning
the status of monitoring programmes in the various WHO
Regions, are summarized in Table 4.
Table 4:
Current status of monitoring activities and
laboratory facilities in IDD-affected
countries (1999)
|
WHO Regions |
Number of IDD-affected countries |
Number of IDD-affected
countries |
||
|
Monitoring salt quality |
Monitoring Iodine status |
With laboratory
facilities |
||
|
|
44 |
29 |
24 |
28 |
|
The |
19 |
19 |
19 |
19 |
|
|
9 |
8 |
7 |
6 |
|
|
32 |
17 |
13 |
23 |
|
|
17 |
14 |
10 |
11 |
|
Western Pacific |
9 |
8 |
6 |
7 |
|
Total |
130 |
95 |
79 |
84 |
|
Per cent |
100% |
73% |
61% |
65% |
*These figures
reflect countries with the capacity
for both urinary iodine and/or salt iodine level
analyses. Standard of laboratories and expertise for each of these,
however, is very different.
Challenges for the future: consolidating the achievement
It is clear that, despite the great success
in many
countries, there remain challenges for the future.
* Continued
and strong government commitment
and motivation, with appropriate
annual budgetary allocations to
maintain the process, are
essential to eliminate IDD.
* The salt industrly should have the mandate
and the access to resources to ensure effective iodization. Producer
compliance, quality assurance, logistical problems, and bottlenecks
needs to
be
addressed through effective advocacy and social communications.
* Monitoring systems should be in place to
ensure specified salt iodine content, and
should be coordinated
with effective regulation and
enforcement.
* Small-scale producers need to be included in
this process, to ensure that their products are also brought up to standard
and that they deliver the right
amount of iodine to the population. This
is often best achieved by the formation of cooperatives or through working with a common distributor,
thus reducing the need for many small iodization units.
* In some countries, salt for animal
consumption has not been included
in the iodization programme and is not covered
by legislation. Animal
productivity is also enhanced by elimination of
IDD. Ensuring this salt is
iodized also means eliminating leakage of
uniodized salt into
the market and
resultant consumption by the general population.
* There
are still numerous places in the world
where iodized salt is not
available. Identifying these areas and
developing in them a market for iodized salt is critical to
successful IDD elimintion. This process includes creating consumer
awareness and demand.
Esuring the required daily intake of iodine to maintain
normal brain function is an
important as the provision of clean
water. There is adequate
knowledge and expertise to ensure the sustained elimination of IDD from the
entire world.
Thus, an ancient scourge of mankind can be
eliminated with the application of
existing technology. The
achievement of the sustained
elimination of IDD will
constitute one of the major public health triumphs of our
time.
Indicators of the salt iodization process
Factors that determine salt iodine content
Iodization may
take place inside
the country at
the main production or packing
sites, or outside the country by
importing salt which has already been iodized. Salt is
iodized by the addition
of fixed amounts of potassium iodate, as either a dry
solid or an aqueous solution, at the point of production.
Iodate
is recommended in preference to iodine because it is much more
stable (16, 17).
The stability of iodine in salt
and levels of iodization
are questions of crucial importance
to national health authorities and salt producers, as
they have implications for
programme effectiveness, safety, and cost.
The actual
availability of iodine from iodized
salt at the consumer level can vary over a wide range
as a result of:
* variability
in the amount
of iodine added
during the iodization process;
* uneven
distribution of iodine in
the iodized salt
within batches and individual bags;
* the
extent of loss
of iodine due
to salt impurities, packaging, and
environmental conditions during
a storage and distribution; and
* loss of iodine due to food processing, and
washing and cooking processes in the household.
In order
to determine appropriate levels
of iodization, an accurate
estimate is required of the losses of iodine occurring between the
tie of iodization and the time
of consumption. Control of
moisture content in
iodized salt throughout manufacturig and
distributions, by improved
processing, packaging, and storage, is critical to the stability of the
added iodine.
A recent laboratory study (18) examined the
effects of humidity and packaging
materialson the stabiliyt of iodine in typical salt samples from countries with tropical and subtropical
climates. The study
showed that high
humiditym coupled with
porous packaging, resulted in
30-80% loss of iodine within a period of
six months.
The study
also determined that losses
could be significantly reduced (in the range of 10-15%) by using packaging
with a good moisture barrier, such as low-density polyethylene
(LDPE) bags.
However,
longer storage - beyond six months - aggravated losses. Therefore,
it is recommended
that the time
required for distribution, sale and consumption of iodized salt be minimized as far as possible, to ensure
effective use of the added iodine.
Additional
measures can be taken to retain the storage efficiency of low-density
polyethylene films, in a system of high mechanical strength and
resistance to puncture.
Woven high-density
polyethylene (HDPE) bags,
with a continuous film
insert or laminate of low density
polyethylene, should be considered as an
effective low-cost packaging method for iodized salt.
Recommendations
WHO/UNICEF/ICCIDD recommended (19)
that, in typical circumstances, where:
* iodine
lost from salt
is 20% from
production site to household,
* another 20% is lost during cooking before
consumption, and
* average salt intake is 10 g per person per
day,
Iodine
concentration in salt at the point of production should be within the range of
20-40 mg of iodine per kg of salt (i.e. 20-40 ppm of iodine) in order to provide 150 ug of
iodine per person per
day. The iodine should be added
as potassium (or sodium) iodate. Under these circumstances median urinary
iodine levels will vary from 100-200
ug/l.
However, in some instances the quality of iodized salt
is poor, or the salt is incorrectly
packaged, or the salt deteriorates due to
excessive long-term exposure
to moisture, heat,
and contaminants. Iodine losses
from point of
production to consumption can
then be well in excess of 50%. In
addition, salt consumption is sometimes much less than 10 g per person per day.
As a
result, actual iodine
consumption may fall
well below recommended levels.
Regular
surveys of median iodine urinary levels should
therefore be carried out in a
representative sample of the at-risk population, to
ensure that those
levels are within
the recommended range (100-200
ug/l). If not, the level
of iodization of salt, and factors affecting the
utilization of iodized salt,
should be reassessed focusing on:
* salt quality and the iodization process;
* factors affecting iodine losses from salt,
such as packaging, transport, and storage;
and
* food habits in relation to salt intake and
cooking practices.
National authorities
should establish initial
levels for iodization in consultation with the salt industry, taking
into account expected losses
and local salt consumption.
Once iodization has commenced, regular surveys of salt iodine content and
urinary iodine levels should be carried out to determine if the programme is having the desired
effect.
Discussions and
regulations about iodine levels
in salt must clearly
specify whether they refer to
total content of iodine alone or to content of iodine compound
(KIO3 or KI).
It is
recommended that the level be
expressed as content
of iodine alone. This
approach emphasizes the
physiological important component
(iodine) and facilitates comparison
of its different forms.
3.2 Determining salt iodine levels
The
iodine content of salt can be determined quantitatively with the titration method, and qualitatively
using rapid test kits.
Titration method
The
iodine content of salt can be determined by liberating iodine from salt and
titrating the iodine with sodium thiosulphate using starch as an external
indicator. The method od liberating
iodine
from salt
differs depending on whether
salt is
iodized with iodate or iodide.
Details of the method are given in
Annex 1. Facilities for titration are usually
available in a public health or food standards
laboratory. Large- and
medium-scale salt producers
should carry out titration on site.
Titration is
preferred for accurate
testing of salt
batches produced in factories
orupon their arrival in a country, and
in cases of doubt, contestation,
etc. This method is
recommended for
determination of the concentration of iodine in
salt at various levels
of the distribution system where
such accurate testing is
required. Once the method
is established, it is
necessary to adhere
to proper internal and external
quality control measures. However,
the titration method
is time-consuming, and is not
recommended for routine monitoring purposes througout the country.
Rapid test kits
These are
small bottles of 10-50 ml, containing
a stablilized starch-based solution.
One drop of the solution placed on
salt containing iodine (in the
form of potassium iodate) produces a blue/purple coloration. These kits should therefore be regarded as qualitative rather than
quantitative.
Coloration indicates
that iodine is
present, but the concentration cannot
be reliably determined. In cases
where there is suspicion of
alkalinity in the salt sample, a
drop of the `recheck solution' may be used and the test
may be
dropped over the drop of recheck solution to indicate the presence
of iodine (see Annex 1 for further details).
An advantage of rapid test kits is that they can
be used in the field to give an
immediate result. They are therefore
useful to health inspectors
and others who are involved in
carrying out spot checks on food
quality or household surveys.
They may
also play a valuable educational role,
in that they provide
a visible indication that salt actually
is iodized. Accordingly,
they can be used for
demonstration purposes in schools and other institutions. However, because rapid test kits do not
give a reliable estimate of
iodine content (20,
21), results must be backed up by titration.
There are a large number of test kits available
on the
market; moreover, many countries
are currently producing their
own. UNICEF also
supplies countries with test
kits. However, a comprehensive review to assess these kits
is still needed.
Monitoring systems
External
monitoring systems by governments
This
system
is based upon the
establishment of a
law which mandates that all salt
for human and - in most countries,
animal - consumption is iodized.
Details of implementation, inspection, and enforcement are set out in the
regulations. Guidelines for developing regulations are available
(23), and a good example of such a law is the ASIN law in the Philippines
(Annex 6). It is crucial
to state in the regulations the amount
of potassium iodate to be added
at the point of production.
Other
legal requirements should include packaging in polyethylene bags, labelling
to identify the iodine level and the
name and address of the company packaging the salt. The regulation also needs
to designate a government agency or department which will be
responsible for a system of licensing
producers, importers, and
distributors, and inspecting their facilities.
That agency must also be responsible for periodically
checking the quality assurance records that must be kept, and for
spot checking the salt for iodate content. Although monitoring at the production and
household level is considered extremely important, retail outlets also need to
be checked periodically to determine
what is
happening in the salt market and
to ensure that all
sources of salt have been identified. Several
monitoring and inspection systems
have emerged in different countries.
Often this monitoring becomes a function of the
Food and
Drugs Bureau of the Health Ministry.
In other countries, the Ministry
of Industry, or Mines, or Agriculture
has this
responsibility. In the
case of importation of salt, the
Customs Authority is often in charge of checking the
specifications in the importation document, and in some circumstances taking
samples to check the iodate level in the salt.
As
indicated above, the salt testing kits that are used by these government agencies should not be used in
enforcement, as they often give both false positive and false
negative results and the colour
does not always accord well
with titration. Government inspection systems
need to have access to and
use of salt
titration
in a standardized laboratory on a regular basis.
When countries
first began to
introduce salt iodization, inspection systems were used largely to guide salt
iodization programme managers in identifying problems with salt iodization, and were
rarely used for enforcement
purposes. As countries increase the coverage to 50%, these
systems should be strengthen and used
for enforcement against those producers
who fail to comply with the law.
It
is often the less expensive uniodized salt in the market that prevents
the realization of elimination of IDD. Indeed, as the
coverage of iodized salt increases,
special efforts need to be made
to identify the
non-complaint importer, producer
and distributor and systematically eliminate that problem.
Salt must be iodized indefinitely, or until
it is
demonstrated that an adequate iodine
intake is available from other
sources. The infrastructure, together with the annual budget to
support the government inspecion system, must be permanently
established. In order to guarantee this, it is essential that inspection
of iodized salt be integrated into the existing
food inspection system in the
country.
Internal monitoring systems by producers and distributors
For each
type of salt production, and for
each type of
salt iodization system, there must be established a set of guidelines for best manufacturing processes. It is the
responsibility of the producer
to have such a set of
guidelines for his
own facility, as each has its own unique characteristics.
The Ministry
of Industry, the Bureau of Standards,
or Codex Alimentarius are useful reference sources for guiding producers in
the process of iodization salt.
They can also esatblish the
ultimate standards expected in the production of iodized salt.
Adherence to these manufacturing standards is perhaps the
most important issue in the
elimination of IDD.
Therefore, the producer plays a pivotal role both in improving the
accuracy of the iodization
process and in
reducing the considerable variations observed in iodine
concentration in many countries.
Among the areas of greatest concern (24) is
the very
important mixing or spraying step.
This area includes not only the
actual iodization method chosen
by a production or packaging facility,
but also the assurance that the producer closely
adheres to the amount of time for
mixing.
Repid test kits should be used frequently during
shifts and, in addition, samples should be taken on a periodic basis for
salt titration. The iodine concentration of each batch
should be checked at least once.
For this
reason, it is recommended that
whenever possible at least
two persons at a production plant
should be trained and their
skills standardized to
determine accurately the
iodine concentration using the
tiration method. Furthermore, key persons
at each production
site should be
aware of the detrimental conseqences of iodine
deficiency and excess, as well as the
health benefits of correctly iodized salt.
Results should
be recorded and plotted in a
quality assurance chart. When levels are not satisfactory, immediate
corrective action should be taken
and that action entered into the record
book.
Because production methods and factory sizes vary so
widely, it is beyond the scope of this
manual to define this process in any
greater detail. Whatever the method
adopted, it should result in salt that has an iodate level that corresponds to
that indicated on the label.
That level should, of course, correspond
to the level allowed for under
the law.
When importers
and distributors procure
salt, they have
the responsibility either to
ensure that it meets specifications as
stipulated in the requirements, or to
ensure that these are met before salt
goes out to the wholesale or retail
market. This implies that
they should have a quality assurance
system that includes salt iodine
titration measurements.
If
the salt they receive is not up to standard, they will need to have their
own iodization facility.
All salt should
be distributed in polyethylene bags, with appropriate
labels as described above.
Monitoring at the household level
There
are two basic methods for obtaining household-level data:
* Cross-sectional surveys; and
* Community-based monitoring.
Cross-sectional surveys
Cross-sectional surveys are conducted infrequently (see Chapter 5: Survey methods). A household questionnaire concerning the use
of iodized salt and qualitative testing of that salt using a salt testing kit has been employed successfully to
determine overall coverage of iodized salt and to identify geographic
gaps in the programme.
This
questionnaire was included in the UNICEF Multiple Indicator Household Cluster Survey (MIHCS) in
1996, and will be repeated in the
next round. Some countries have successfully
added the questionnaire to
other national surveys,
e.g., to either nutrition surveys or surveys that
collect key economic and census data.
These surveys provide estimates of the proportion of the population using
adequately iodized salt, and
identify areas where there is
low use of iodized salt and/or where all the
salt is uniodized.
The results
allow for visual representations of
variations of coverage and
provide a basis for targeting resources and focusing interventions in areas
where they are most needed. This
type of
monitoring should
then be followed
by specific action
to identify further the
reason for low iodized salt usage,
and should result in a
range of actions to correct the
problem. Survey approaches
that have been
successfully used include Cluster Sampling, Lot Quality Assurance Sampling, and
sentinel sample sites (25).
Community-based monitoring
Ongoing household-level monitoring is used more
frequently than periodic surveys.
This approach may
be organized in
the community or through the schools, particularly in areas with high
rates of
school enrolment. Providing
salt testing kits
to environmental health officers,
community midwives, nutrition officers, schoolteachers, mayors, and other government
workers
responsible for
community health, has been
helpful in this process.
These approaches are very effective communication
and awareness creation tools,
particularly when this awareness is
linked to action. This action could involve approaching the
salt producers
or distributors, and directly requesting them to
supply iodized salt.
Finally,
the occurrence of parallel markets in uniodized salt has frequently been a
barrier to achieving universal salt iodization.
National cross-sectional household
surveys and community monitoring have often been useful
in identifying such salt and in developing strategies to address the problem.
Figure 2
illustrates graphically the
components of a USI
monitoring system. General standards and
specific practices can be checked
by inspections, tests, and records
to assure that
responsible producers
comply with the standards, and
various actions can be taken according to the level of that compliance.
Figure 3
demonstrates a double loop which
can be effectively established among
national or provincial
programmes and community-level
monitoring, through their respective actions
and the resultant feedback.
Programmes take actions, which result in feedback, which aids and
reinforces their activities. Similarly,
monitoring enables actions,
providing feedback to
enhance monitoring.
Once begun, the process is continuous and
self-reinforcing. By their activities, IDD programmes enable
certain assessment and corrective actions.
These actions can result in the
desired effects, which will
in turn assist
programmes in better performing their respective tasks,
and so on around the loops.
Indicators of impact
Overview
Assessment of
thyroid size by palpation is the
time-honored method of assessing IDD prevalence. However, because of the long response time after
iodine supplementation is
introduced this method is
of limited usefulness in assessing
the impact of programmes
once salt iodization has
commenced. In this
case, urinary iodine is the most useful indicator because it is highly sensitive to recent changes in iodine
intake.
Since most countries have now started to
implement IDD control programmes, urinary iodine rather
than thyroid size is emphasized in
this manual as the principal
indicator of impact. Thyroid size is more useful in the baseline
assessment of the severity of IDD,
and also has a role in the assessment of
the long-term impact of control
programmes.
The
introduction of ultrasonography for the precise assessment of thyroid size has been a significant development. However,
this approach requires costly equipment and a source of electricity in
the field. Moreover, there are as yet no
generally accepted standards for
thyroid size in iodine-replete populations.
Two other
indicators are included in this discussion: thyroid stimulating hormone (TSH) and thyroglobulin (Tg). While TSH
in neonates are particularly
sensitive to iodine
deficiency, difficulties in interpretation remain. Furthermore, the cost of implementing a
screening programme is
too high for
most developing countries. The
value of thyroglobulin as an indicator of
IDD status has yet to be fully explored and to
gain wide acceptance.
Urinary Iodine
Biological features
Most
iodine absorbed in the body eventually appears in the urine. Therefore,
urinary iodine excretion is a
good marker of
very recent dietary iodine
intake. In individuals, urinary
excretion
can vary somewhat from day to day and even within
a given
day. However, this variation
tends to even out among populations.
Studies have convincingly demonstrated that a profile
of iodine concentrations in morning or
other casual urine specimens (child or adult)
provides an adequate
assessment of a
population's
iodine nutrition, provided a sufficient number of specimens is collected.
Twenty-four hour samples are difficult to obtain and are not necessary.
Relating urinary iodine to creatinine is
cumbersome, expensive, and unnecessary.
Indeed, urinary iodine/ceatinine
ratios are unreliable, particularly when protein intake - and consequently
creatinine
excretion - is low.
Feasibility
Acceptance of this
indicator is very
high, and spot
urine specimens are easy to
obtain. Urinary iodine assay
methods are not difficult
to learn or use
(see below), but
meticulous attention is required
to avoid contamination with iodine at
all stages. Special laboratory
areas, glassware, and reagents should be set aside solely for this
determination.
In general,
only small amounts
(0.5-1.0 ml) of urine
are required, although the exact volume depends on the method. Some urine
should also be kept in reserve.
Samples are collected in tubes, which should be tightly sealed with screw
tops. They do not require refrigeration, addition of
preservative, or immediate determination
in most methods.
They can be
kept in the laboratory for months for more, preferably in a
refrigerator to avoid unpleasent odour.
Evaporation
should be avoided, because this process artifactually increases the concentration. Samples may safely be frozen
and refrozen, but must be
completely defrosted before
aliquots are taken for analysis.
Many analytical
techniques exist, varying from
very precise measurement with
highly sophisticated instruments,
to semi-quantitative `low
tech' methods that can be used
in regional,
country or local laboratories. Most methods
depend on iodide's role
as a catalyst in the reduction of
ceric ammonium sulfate
(yellow colour) to the cerous
from (colourless) in the presence
of arsenious acid (the Sandell-Kolthoff
reaction). A digestion or
other purification step using ammonium persulfat or
chloric acid is necessary before
carrying out this reaction, to rid the
urine of interfering contaminants.
A brief
description of some of the methods introduced in
this section is presented in the following pages.
* Methods with ammonium persulfate (Method A)
Small samples of urine (250-500 ml) are
digested with ammonium persulfate at 90-110 C; arsenious
acid and ceric ammonium sulfate are then added.
The decrease in yellow colour over a fixed time period
is then measured by
a spectrophotometer and
plotted against a standard curve constructed with known amounts of iodine
(26). This method
requires a heating
block and a spectrophotometer, which are both
inexpensive instruments. About 100-150 unknown samples can be run in a day by one
experienced technician. Several
versions of this method exist:
details of one of these are given
in Annex 3.
* Methods with chloric acid (Method B)
Chloric acid can be substituted for ammonium
persulfate in the digestion step, and the colorimetric
determination carried out as for method A (27).
A disadvantage is the safety concern, because the chemical
mixture can be
explosive if residues
dry in ventilating sytems. Handlings these chemicals in a fume cupboard
and using a chloric acid trap when performing sample digestion is strongly
recommended (see Annex 3).
* Other methods
A
modification of Method B uses the rebox indicator ferroin and a stopwatch
instead of a spectrophotometer to measure colour change (28). Urine is digested with chloric acid and
colour changes in batches of samples
measured relative to standards of known iodine content. This
places samples in categories (e.g.,
below 50 ug/litre, 100-200
ug/l, etc.) that can be adjusted
to desired levels. This
method is currently being adapted
to ammonium persulfate digestion.
Another
semi-quantitative method is based on the iodide-catalyzed oxidation of
3,3`,5,5`-tetramethylbenzidine
by peracetic acid/H202 to
yield coloured products that are recognized on a
colour strip indicating three ranges:
<100 ug/l, 100-300 ug/l, and
>300 ug/l (22). Interfering
substances are removed by pre-packaged columns with activated charcoal. Analyses must be run
within two hours, and the procedure requires
the manufacturer's pre-packed columns.
* Other methods (continued)
In still
another method, samples are digested
with ammonium persulfate on microplates enclosed in specially
designed sealed cassettes and heated to
110 C (29). Samples are then transferred
to another microplate and the ceric
ammonium sulfate reduction reaction carried
out and reach on a microplate
reader. Field tests are promising: up to 400 urine samples can be
analysed in one day, depending on
manufacturers' supplies.
Choice of method
Criteria for assessing urinary iodine methods are
reliability, speed,
technical demands, complexity
of instrumentation,
independence from sole-source suppliers,
safety, and cost. The
choice among the above and other methods depends on
local needs and resources.
Large central laboratories
processing many samples may
prefer `high-tech' methods, while smaller
operations
closer
to the field may find the simplest methods more practical.
Due to the
potential hazards of chloric acid,
Method A using ammonium persulfate is currently
recommended. It can adequately replace the chloric acid method,
since the main differnce is the substitution of
ammonium persulfate for
chloric acid in the
digestion step (see Annex 3). Results
are comparable.
The other methods described above show promise
but are not yet fully tested.
Quality control and reference laboratories
All laboratories
should have clearly defined
internal quality control procedures
in place, and should be open
to external audit. In addition, all laboratories should
participate in an external
quality control programme
in conjunction with
a recognized reference laboratory.
Active efforts are now in progress, both to define
performance criteria for laboratories
and to develop a global system
of reference laboratories. These
reference laboratories will provide reliable measurements of
urinary iodine, and will conduct technical
training and supervision. This initiative is a
major priority for ensuring sustainability of iodine sufficiency.
Performance
Most
of the above methods perform reliably, although some of the newer
ones need further testing as of this date.
All these methods routinely
recognize urinary iodine concentrations in
the
range
of 50-200 ug/l.
With appropriate
dilutions, they can be
extended upward to examine whatever range is desired. The coefficient of variation is
generally under 10% for all methods. Proper
training is necessary but not
complicated.
Since casual
specimens are used, it is desirable to
measure a sufficient number from a given population to allow for
varying degrees of subject hydration and other
biological variations among individuals,
as well as to obtain a
reasonably narrow confidence interval
(see Annex 4).
In general, 30
urine determinations from a defined sampling group are sufficient.
Interpretation
Simple
modern methods make it feasible to process large number of samples at low cost
and to characterize the distribution according to different cut-off points and intervals. The
cut-off points
proposed
for classifying iodine nutrition into different
degrees of public health significance are shown in Table 5.
Frequency distribution curves
are necessary for
full interpretation.
Urinary iodine values
from populations are usually
not normally distributed.
Therefore, the median rather than
the mean should be used as the measure of central tendency.
Likewise, percentiles rather than
standard deviations should be used as
measures of spread.
Median
urinary iodine concentrations of 100 ug/l and above define a population which
has no iodine deficiency, i.e. at least 50% of the sample should be above 100
ug/l. In addition, not more than 20% of samples should be below 50 ug/l.
Alternatively,
the first quintile (20th percentile) should be
at least 50 ug/l. In adults, a
urinary iodine concentration of 100 ug/l
corresponds roughly to a daily iodine intake of about 150 ug under steady-state
conditions.
Urinary iodine
concentration is currently
the most practical biochemical marker for iodine nutrition, when
carried out with appropriate technology
and sampling. This approach
assesses
iodine
nutrition only at the time of measurement, whereas thyroid size reflects iodine
nutrition over months or years.
Therefore, even though
populations may have attained iodine sufficiency by median urinary iodine concentration,
goitre may persist, even in children.
With rapid
global progress in correcting
iodine deficiency, examples of
iodine excess are being recognized,
particularly when salt iodization is excessive and poorly
monitored (21). Tolerance
to high doses of iodine is quite
variable, and many individuals ingest amounts of several milligrams
or more per day without apparent
problems.
The major
epidemiological consequences of
iodine excess is iodine-included hyperthyroidism (IIH) (30,
31). This occurs more commonly in older
subjects with pre-existing nodular goitres, and
may
occur even when iodine intake is within the normal range.
Iodine intakes
above 300 ug/l per
day should generally
be discouraged, particularly in
areas where iodine deficiency has previously existed. In these situations, more individuals may be
vulnerable to adverse health consequences,
including iodine-included hyperthyroidism
and autoimmune thyroid diseases.
In populations characterized by
longstanding iodine deficiency and rapid increment in iodine
intake, median value(s) for urinary iodine above 200 ug/l are not recommended
because of the risk of
iodine-included hyperthyroidism. This
adverse condition can occur
during the 5 to 10 years
following the introduction
of iodized salt (30, 31). Beyond
this period of time, median values up to
300 ug/l have not demonstrated side-effects, at least not in populations with adequately iodized
salt.
Thyroid size
The
traditional method for determining thyroid size is inspection and palpation.
Ultrasonography provides a more
precise and objective method.
However, there is no agreement
on reference values.
Both
methods are described below. Issues
common to palpation and ultrasound are not repeated in the section on
ultrasound.
Thyroid size by palpation
The size of the thyroid gland changes inversely
in response to alterations in
iodine intake, with a lag interval
that varies from a few months to several years, depending
on many
factors. These include the
severity and duration of iodine deficiency, the type and effectiveness of iodine supplementation,
age, sex, and possible additional
goitrogenic factors.
The term
"goitre" refers to a thyroid gland that is
enlarged. The statement that "a thyroid gland each of
whose lobes have a volume
greater than the terminal phalanges of the thumb of the
person examined will be considered goitrous" is empirical but has
been used in most epidemiological
studies of endemic goitre and is still
recommended (see Table 6).
Feasibility
Palpation of the
thyroid is particularly useful in
assessing goitre prevalence, but
much less so in determining
impactl. Costs are associated
with mounting a survey, which is
relatively easy to conduct, and training of personnel. These
costs will vary depending
upon the availability of health
care personnel accessibility of
the populations, and samples size.
Feasibility and performance vary according to target groups, as follows:
Neonates: It is neither feasible nor practical to
assess goitre among neonates, whether by
palpation or ultrasound. Performance is
poor.
School-aged
children (6-12 years): This is the
preferred group, as it is usually
easily accessible. However,
the highest prevalence of goitre
occurs during puberty and childbearing
age. Some studies have focused on
8-10 years.
There is a
practical reason for not measuring
very young age groups.
The smaller the child, the smaller the thyroid, and the more difficult it is to perform
palpation.
If
the proportion of children attending school is less than 50%, school children may not be
representative. In these cases, spot surveys
should be conducted among those
who attend school and those
who do not, to ascertain if there
is any significant difference between the two.
Alternatively, children
can be surveyed in
households. For further
discussion, see Chapter 5 on Survey Methods.
Adults: Pregnant and lactating women are of
particular concern. Pregnant
women are a
prime target group
for IDD control activities because
they are especially
sensitive to marginal iodine deficiency.
Often they are relatively
accessible given their
participation in antenatal clinics.
Women of childbearing age - 15-44
years - may be surveyed in households.
Technique
The subject to be examined stands in front of the
examiner, who looks carefully
at the neck for any sign of
visible thyroid enlargement. The subject is then asked to look up and
thereby to fully extent the neck. Thus
pushes the thyroid forward and makes any enlargement more obvious.
Finally, the
examiner palpates the thyroid
by gently sliding his/her own
thumb along the side of the trachea (wind-pipe) between the cricoid cartilage and the top of the
sternum. Both sides of the trachea are checked. The size and
consistency of the thyroid gland
are carefully noted.
If necessary, the subject is asked to swallow
(e.g. some water) when being examined - the thyroid moves up on swallowing.
The size of each lobe of the
thyroid is compared to the size of the
tip (terminal phalanx)
of the thumb
of the subject
being examined. Goitre is
graded according to the
classification presented in Table 6.
Table 6: Simplified classification of goitre* by
palpation
Goitre 0
No palpable or visible goitre
Goitre 1
A goitre that is palpable but not visible when the
neck is in the normal position,
(i.e., the thyroid
is not visibly enlarged). Thyroid nodules in a
thyroid which is otherwise not enlarged fall into
this category.
Goitre 2
A swelling in the neck that is
clearly visible
when
the neck is in a normal
position and is
consistent with an enlarged thyroid when the neck
is palpated.
* A thyroid gland will be considered goitrous
when each lateral lobe has a volume
greater than the terminal phalanx of the thumbs of the subject being examined.
The
specificity and sensitivity of palpation are low in grades 0 and 1 due to a high inter-observer
variation. As demonstrated by studies of
experienced examiners, misclassification can be high.
Interpretation
Table 7 gives the epidemiological criteria for
establishing IDD severity, based on
goitre prevalence in school-age children.
The terms mild, moderate,
and severe are relative and should
be interpreted in context with information from other indicators.
It is recommended that a total goitre rate or
TGR (number with goitres
of grades 1 and 2 total examined) of 5%
or more in schoolchildren 6-12 years of age be used to signal the presence of a public health problem. This recommendation is based on the observation that
in normal, iodine-replete populations,
the prevalence of goitre should
be quite low. The cut-off point of 5% allows both for some margin of error of
goitre assessment, and for goitre that
may occur in iodine-replete populations
due to other causes such as
goitrogens and autoimmune thyroid diseases.
Table 7. Epidemiological
criteria for assessing
the severity of IDD based on the prevalence of goitre
in school-aged children
Degrees
of IDD, expressed as percentage of
the total of the number of
children surveyed
|
|
None |
Mild |
Moderate |
Severe |
|
Total goiter rate (TGR)
|
0.0-4.9% |
5.0-19.9% |
20.0-29.9% |
>-30% |
Finally
in this connection, it is emphasized that thyroid size in the community may not
return to normal for months or years
after correction of iodine deficiency.