The document discusses thyroid function tests (TFTs), which measure how well the thyroid gland is working. Major TFTs include serum thyroid stimulating hormone (TSH), free thyroxine (T4) and triiodothyronine (T3), total T4 and T3, and tests for autoimmune thyroid diseases. TSH is the most sensitive and reliable test, with high levels indicating hypothyroidism and low levels indicating hyperthyroidism. Elevated or low T4 and T3 also help diagnose hypo- or hyperthyroidism. The tests help diagnose thyroid disorders, screen newborns, and monitor thyroid replacement therapy.

1. By
Dr. Santhosh Kumar N
Associate Professor
Department of Biochemistry

2. Butterfly-shaped endocrine gland,
located in the lower front of the neck
It absorbed iodine from the circulating
blood & combine with tyrosine of
thyroglobulin to form TH
Thyroid gland release
- Thyroxine (T4) &
- Tri-iodothyronine (T3)

3. Increased metabolic rate (Calorigenic effect)
Maintenance of blood pressure
Regulates enzyme activity system
Heat production & Body temperature
Maintain growth & development
Regulates the rate of metabolisms (CH’s,
Lipids & Proteins)
Functions

4. Thyroid Function Tests (TFTs)
A series of blood tests used to measure
how well thyroid gland is working.

5. Diagnosing thyroid disorder in symptomatic person
Screening newborns for hypothyroidism and adults for
thyroid disorders
Monitoring thyroid replacement therapy in hypo-
thyroidism patients
Diagnosis & monitoring female infertility patients
Purpose
of
TFTs

6. Major Thyroid Function Tests
• Serum Thyroid Stimulating Hormone (TSH)
• Serum free Thyroxin (T4 )& Tri-iodothyronine (T3 )
• Serum Total T4 & T3
• Radioactive iodine uptake (RAIU) test
• Estimation Of Serum Cholesterol
• Tests for autoimmune thyroid diseases include tests
– Anti-TSH receptors antibodies
– Anti-thyroglobulin antibodies
– Anti-microsomal antibodies
– Anti-thyroperoxidase antibodies

7. Serum Thyroid Stimulating Hormone (TSH)Test
• Sensitive, specific and reliable test of thyroid status.
• Stimulation of thyroid gland by the TSH will causes the release of
stored Thyroid hormones.
• When T4 & T3 are too high - TSH secretion decreases
• When T4 & T3 are too low, - TSH secretion increases
• Useful diagnosis of primary hypothyroidism (TG failure)

8. Normal value : 0.25 to 5.5 μIU/ml
High TSH level Low TSH level
Thyroid gland is failing – Primary
hypothyroidism due to absence of –ve
feedback control on PG
- Addison’s disease,
- Pituitary adenoma.
Overactive thyroid gland
- Primary hyperthyroidism,
-Secondary hypothyroidism
(Anterior pituitary failure)
- Tertiary hypothyroidism
(hypothalamic failure)
TSH estimated by - Radioimmunoassay

9. Serum Free T4 & T3
• Metabolically active & measures useful in condition by where TBG levels
are affected.
• Free TH conc. provide more reliable, of diagnosing thyroid dysfunction
than measurement of total serum T4 & T3
• Normal serum Free T4 : 9.0 to 24.0 pmol/L
serum Free T3 : 4.0 to 8.0 pmol/L
• Elevated T4 & T3 in hyperthyroidism. Low level seen in hypothyroidism.

10. Serum Total T4 & T3
• Total thyroid hormones includes free as well as protein bound.
• levels of total thyroxin are affected by changes in levels of TBG in the absence of
thyroid diseases
• Normal serum total T4 : 5 to 12 μg/dL
serum total T3 : 0.60 to 2.15 ng/dl

11. - Increased hormone secretion is seen in states of hyperthyroidism,
(raised conc. of TBG- in pregnancy & with estrogen therapy)
- Decreased in serum occurs in cases of hypothyroidism,
(decrease conc. of TBG- in nephrosis due to loss of TBG in urine &
liver disease (decreased syn of TBG )
• T4 combined with TSH test gives the best measurement of thyroid
function

12. Radioactive iodine uptake (RAIU) Test
• It measures, how much RA-I is taken up by the thyroid gland in a certain
period but does not involve imaging.
• Similar test is the thyroid scan.
• These two tests are commonly performed together.

13. Giving a radiotracer (containing radioactive
iodine eg; I123 or I131) is either injected (liquid)
into the body, swallowed (capsule) or inhaled
as a gas.
Radiotracer accumulates in the organ or area of
the body being examined
After 4 to 6 hours and again 24 hours. using a
gamma probe to check the amount of
radioactivity in the thyroid gland

14.  It show, how much of this radioactive iodine is absorbed by the thyroid.
In normal responses for 4-6 hours: 3 -16% and 24 hours: 8 -25%
Higher- uptake Lower-uptake
Overactive thyroid gland
- Graves disease
- Enlarged thyroid gland
- Toxic nodular goiter
- Post thyroiditis
- Thyrotoxicosis
Hypothyroidism
Sub-acute thyroiditis
Painless thyroiditis

15. Estimation Of Cholesterol In Serum
• It is a useful index in monitoring the effectiveness of the therapy in
thyroid condition.
• Increased cholesterol levels seen in hypothyroidism because
cholesterol carrying lipoprotein degradation is decreased

16. Thyroid auto-antibodies
• helps to demonstrate the presence of the auto immune disorders
• Graves’ disease is associated with presence of anti-TSH-receptor Ab.
• Thyroiditis is associated with the presence of anti-thyroid peroxidase
Ab (anti-microsomal antibodies)
• Thyroid peroxidase and thyroglobin antibodies – immunological
mediated thyroid disease.

17. PATTERN OF DIAGNOSIS FOR THYROID DISORDERS

18. CLINICAL SIGNIFICANCE OF THYROID HORMONES
Hypothyroidism Hyperthyroidism
Primary
Secondary
Tertiary
Causes:
- Iodine deficiency,
Excess iodine intake & thyroiditis
-Hypopituitarism – adenoma,
Destruction of pituitary
-- Hypothalamic dysfunction
Causes:
- Grave’s disease
- Multi-nodular goiter
- Thyroid destruction
- Metastatic thyroid
carcinoma
Symptoms:
- Weight gain, Lack of energy, Confusion,
Symptoms:
Weight loss, Fatigue,

19. Case report - 01
Following is the laboratory report of a patient
Report Normal Ranges
Serum T3 : 250 ng/dl (120 to 190 ng/dl)
Serum T4 : 20 μg/dl (5 to 12 μg/dl)
Serum TSH : 0.01 μU/ml (0.5 to 5.0 μU/ml)
Q: a) What is the probable diagnosis?
b) What are clinical features associated with this condition?
c) What are the other investigations suggested for this patient?

20. a) What is the probable diagnosis?
Hyperthyroidism (Over activity of thyroid gland)
b) What are clinical features associated with this condition?
• Causes: Grave’s disease, Multi-nodular goiter and Metastatic thyroid carcinoma
• Symptoms: elevated BMR, tachycardia, Weight loss, Fatigue, sleeplessness
Nervousness, Heat intolerance, excessive sweating, muscle weakness &Tremors
c) What are the other investigations suggested for this patient?
• Basal metabolic rate (BMR),
• Serum cholesterol and
• Radioiodine uptake test & Thyroid scan help to determine why thyroid is overactive:
• Detection of auto-antibodies (thyroid stimulating IgS or long acting thyroid
stimulators(LATS)

21. Case report – 02
Following is the laboratory report of a patient
Report Normal Ranges
Serum T3 : 90 ng/dl (120 to 190 ng/dl)
Serum T4 : 2.5 μg/dl (5 to 12 μg/dl)
Serum TSH : 20 μU/ml (0.5 to 5.0 μU/ml)
Serum Cholesterol: 300 mg/dl (150-200 mg/dl)
Q: a) What is the probable diagnosis?
b) What are clinical features associated with this condition ?
c) What dietary advice should be given to the patient
d) Why does hypothyroidism cause hypercholesterolemia in the above condition

22. a) What is the probable diagnosis?
Hypothyroidism
b) What are clinical features associated with this condition ?
Causes: Primary - Iodine deficiency, Excess iodine intake & thyroiditis
Secondary: Hypopituitarism – adenoma, destruction of pituitary
Tertiary- Hypothalamic dysfunction
Symptoms: Tiredness, Weight gain, intolerance of cold conditions, hoarseness of voice,
hair loss, constipation, depression, bradycardia, dry skin. puffy face & Low motor
activity.
Cretinism (Neonatal hypothyroidism)– multiple congenital defects & mental retardation
.
Myxoedema (In adults) with puffiness of the face, bagginess under eyes, slowness in
physical activities and overall weight gain

23. c) What dietary advice should be given to the patient
Consumption of iodized salt and to avoid goitrogenic foods eg. Cabbage and
cauliflower
d)Why does hypothyroidism cause hypercholesterolemia in the above
condition
- Low thyroid hormones, cannot process as much of cholesterol in the liver .
- Body removes less LDL cholesterol from the blood lead to high levels of
LDL and total cholesterol.

24. Have a great day to all
Thank you
Next : AFTs