The document provides information about thyroid function tests: - The thyroid gland regulates vital body functions through its hormones T3 and T4. Thyroid disorders are common worldwide and in India, with an estimated 42 million Indians suffering from thyroid disease. - Thyroid function tests (TFTs) include TSH, FT4, and FT3 levels and are used to diagnose thyroid disorders, monitor treatment, and screen at-risk groups like pregnant women. TSH is usually the initial test used. - Hyperthyroidism causes anxiety and tremors while hypothyroidism causes fatigue and depression. Certain drugs and illnesses can impact TFT results so clinical context is important when interpreting them. Communication between doctors and

1. THYROID FUNCTION
TEST
Dr. Suman Mukherjee
1st Year MDS
V.S.D.C.H.

4. Contents :
• Introduction
• Thyroid Epidemiology
• Thyroid gland
• Thyroid gland function
• How the Thyroid gland work ?
• Why do you need a thyroid gland
• Hyperthyroidism
• Hypothyroidism
• Classification of TFT
• Range of tests avl.
• Indications of TFT
• When to test
• Reflex testing

5. Introduction :
Thyroid diseases are, arguably, among the commonest endocrine
disorders worldwide. India too, is no exception. Thyroid diseases are
different from other diseases in terms of their ease of diagnosis,
accessibility of medical treatment, and the relative visibility that even a
small swelling of the thyroid offers to the treating physician. Early
diagnosis and treatment remain the cornerstone of management.

6. Thyroid epidemiology :
According to a projection from various studies
on thyroid disease, it has been estimated
that about 42 million people in India suffer
from thyroid diseases, with 90% of them
being undiagnosed.
- Indian Thyroid Society (2010)
Thyroid disorders in India: An epidemiological perspective
U.G.Ambika M.V.Usha
Indian J Endocrinol Metab. 2011 Jul; 15(Suppl2): S78–S81.

7. Thyroid Gland
The thyroid gland is a butterfly-shaped organ
located in the base of your neck. The thyroid
gland is about 2-inches long and lies in front of
your throat below the prominence of thyroid
cartilage sometimes called the Adam's apple.
The thyroid has two sides called lobes that lie
on either side of your windpipe, and is usually
connected by a strip of thyroid tissue known as
an isthmus. Some people do not have an isthmus,
and instead have two separate thyroid lobes.

8. Thyroid gland
functions :
The thyroid's hormones regulate vital body
functions, including:
• Breathing
• Heart rate
• Central and peripheral nervous systems
• Body weight
• Muscle strength
• Menstrual cycles
• Body temperature
• Cholesterol levels
• Much more!

9. Why You Need a Thyroid Gland :
T3 and T4 travel in your bloodstream to reach almost every cell in the
body. The hormones regulate the speed with which the cells/metabolism
work. For example, T3 and T4 regulate your heart rate and how fast
your intestines process food. So if T3 and T4 levels are low, your heart
rate may be slower than normal, and you may have constipation/weight
gain. If T3 and T4 levels are high, you may have a rapid heart rate and
diarrhea/weight loss.

10. Hyperthyroidism :
• Anxiety
• Irritability or moodiness
• Nervousness, hyperactivity
• Sweating or sensitivity to high
temperatures
• Hand trembling (shaking)
• Hair loss
• Missed or light menstrual periods

11. Hypothyroidism :
• Trouble sleeping
• Tiredness and fatigue
• Difficulty concentrating
• Dry skin and hair
• Depression
• Sensitivity to cold temperature
• Frequent, heavy periods
• Joint and muscle pain

14. Range of tests available
TSH (thyroid stimulating hormone, thyrotropin)
FT4 (free thyroxine)
FT3 (free triiodothyronine)
Thyroglobulin
Thyroid autoantibodies
Thyroid stimulating antibody

15. Indications for TFT:
• Diagnosing thyroid disorder in
symptomatic patients.
• Screening new born for
hypothyroidism.
• Monitoring thyroid replacement
therapy in hypothyroidism patients.
• Diagnosing and monitoring female
infertile patients.
• Screening adults for thyroid.

16. Bpacnz recommends
• Asymptomatic patients are not screened
for thyroid.
• TSH is used as the sole test for thyroid
function in most situations.

17. Why not screening for all patients ?
Patients with no symptoms of thyroid disease and no obvious risk factors
have a low likelihood of thyroid disease.
In most situations, TSH is the more sensitive indicator of thyroid status.
If further thyroid function tests are indicated they can be
subsequently added by the laboratory, or the GP usually without the
need to retest the patient.

18. When to test ?
• In 1997, Bandolier revisited a 1978 study which emphasised the
importance of clinical examination and history as the most significant
factors when deciding to request thyroid function tests.
• Although some patients are at increased risk of thyroid dysfunction,
screening is not recommended unless there are signs and symptoms of
thyroid disease.

19. Reflex testing
• Laboratories retain blood samples for varying lengths of time, making it
possible to add additional tests without the need for another blood
sample.
• If further testing is indicated by the result of the TSH test some
laboratories will add FT4, FT3 and thyroid antibodies (this is called
‘reflex testing’). However, we do not recommend GPs rely on the
laboratory to add extra tests.

20. Limitations of thyroid function tests
Thyroid function tests are measured by immunoassays that use specific
antibodies and are subject to occasional interference. Results should be
interpreted in the context of the clinical picture.
If the laboratory results appear inconsistent with the clinical picture,
communicate this to the laboratory and request the following checks:
Confirm the specimen identity.
Reanalyse the specimen using an alternative manufacturer’s assay.
Analyse the specimen for the presence of a heterophilic antibody.
When you are unsure of the relevance of a particular result, a phone call to the
pathologist can be extremely helpful.

21. Thyroid tests in the pregnant patient
Thyroid screening in women planning pregnancy, and those who are pregnant,
has been advocated by some groups. At this stage screening these groups
remains controversial and is not recommended, unless there are symptoms of
thyroid disease.
TSH may be temporarily suppressed during the first trimester of pregnancy,
due to the thyroid stimulating effect of hCG. FT4 levels tend to fall slowly in
the second half of pregnancy.

22. Hypothyroid pregnant patients
In hypothyroid pregnant patients receiving treatment, the goal should be
normalisation of both TSH and FT4. The majority of women receiving
thyroxine need a dose increase during pregnancy, usually during the first
trimester, and a ‘proactive’ dose increase of 30% has been recommended once
pregnancy is confirmed.10
Dose requirements stabilise by 20 weeks, then fall back to non-pregnant levels
after delivery.
FT4 should be maintained above the 10th percentile of the range (about 11-13
pmol/L) from week 6 to week 20.
Thyroid function (especially FT4) should be checked early in pregnancy and at
the start of trimesters two and three. More frequent retesting is sometimes
indicated (e.g. if thyroxine dose is altered).

23. Sick euthyroid syndrome
Acute or chronic non-thyroidal illness has complex effects on thyroid function
tests (sick euthyroid syndrome), and in many cases can make some thyroid
function tests inherently non-interpretable.
During illness, TSH frequently falls, and then may rise temporarily on recovery.
There may also be transient changes in the FT4 and FT3.
It is recommended patients with non-thyroidal illness should have thyroid
function testing deferred until the illness has resolved, unless there is
history or symptoms suggestive of thyroid dysfunction.

24. The effects of drugs on thyroid function
Amiodarone
Thyroid function should be checked prior to commencing amiodarone.
Mildly abnormal thyroid function tests often occur in the first six months of
treatment (mild TSH and FT4 elevation).
Patients on long term therapy should be monitored with 6 monthly TSH and FT4
tests. An early repeat should be arranged if there are abnormalities of
concern (such as falling TSH) or the patient develops symptoms of thyroid
dysfunction.
Lithium
Can lead to hypothyroidism, especially in patients with underlying autoimmune
thyroid disease. An annual check of thyroid function is recommended.

25. GP and laboratory communication
To provide a better outcome for the patient it is important there is open and
clear communication between the GP and the laboratory. It is important the
laboratory is aware of the following:
- The clinical indication for testing
- Any relevant drug treatments the patient may be taking
Providing the laboratory with as much clinical information as possible allows the
laboratory to provide a better service. Reflex tests can be added more
appropriately, and abnormal or unexpected results can be investigated and
interpreted more effectively.

26. New updates
• NAFLD, female , obesity – hypothyroidism s/b ruled out. (metabolic
syndrome)
• Chronic HCV infection in childrens – mimic structure thyroid cells – Anti
TPO, Anti TG overt thyroidism
So screening is mandatory before treatment.
• Steroid responsive nephrotic patients relapse pts may have
hypothyroidism (temporary) because they have oxidative stress in body –
affect kidney – inc. permeability of GBM – loss of TG – low T3 T4 – high
TSH .
Increase remission . No need of thyroid treatment

27. References
• Springer
• Indian thyroid society manual
• Harrison’s principles of internal medicine . 17th edition , pg – 2224- 2246
• Henry clinical diagnosis and management by lab methods 21st edition. Pg –
263 – 279
• Chatterjee MN and Rana shindhe Textbook of biochemistry 7th edition .
JAYPEE. Pg : 638 – 646
• Henry and Todd , Textbook of Clinical Pathology, 22nd edition

28. THANK
YOU