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Dr. Vijay Marakala, MBBS, MD.Senior LecturerBIOCHEMISTRY
IMS, MSU.
THYROID FUNCTION TESTS
THYROID FUNCTION TESTS
Introduction Indications Assay of Hormones
Radio Iodine Uptake
Detection of Thyroid
Antibodies
THYROID FUNCTION TESTS
THE THYROID GLAND IS A BUTTERFLY-
SHAPED ENDOCRINE GLAND THAT IS
NORMALLY LOCATED IN THE LOWER
FRONT OF THE NECK
THYROID FUNCTION TESTS
Laboratory determinations of thyroid function are useful in distinguishing patients with euthyroidism (normal
thyroid gland function) from those with hyperthyroidism (increased function) or hypothyroidism (decreased
function)
DISEASES OF THYROID GLAND
Hypothyroidism Hyperthyroidism
SIGNS AND SYMPTOMS OF HYP0THYROIDISM
Cold intolerance, Bradycardia
Depression
Fatigue, Goiter Hyperlipidemi
a
Weight gain
Dry skin and dry hair,
Myxedema
Menstrual irregularities
SIGNS AND SYMPTOMS OF HYPERTHYROIDISM
Heat intolerance
Fine resting tremor
Tachycardia Palpitations
Anxiety Sleep
disturbance
Irritability
Fatigue
Menstrual irregularitie
s
THYROID FUNCTION TESTS-INDICATIONS
Suspicion of thyroid disease based on clinical signs and
symptomsScreening for
thyroid disease
Evaluation of treatment for thyroid
disease.
BLOOD TESTS TO EVALUATE THYROID FUNCTION
Thyroid-stimulating hormoneTSH
Serum total thyroxineT4
Serum total triiodothyronineT3
Free thyroxineFT4
Free T3FT3
Antithyroid peroxidase antibodies, Antithyroglobulin antibodiesThyroid
antibodies
TSH : THYROID-STIMULATING HORMONE
Elevated TSH (>5 mU/L
hypothyroidism Low TSH (<0.5 mU/Lhyperthyroidism
Normal range: 0.5 – 5mU/L
One of the best thyroid function screening test
T4:SERUM TOTAL THYROXINE
Hypothyroidism• Decreased T4
Hyperthyroidism• Increased T4
Normal range: 65 – 150nmol/L
T3: SERUM TOTAL TRIIODOTHYRONINE
Hypothyroidism• Decreased T3
Hyperthyroidism• Increased T3
Normal range: 1.8 – 3nmol/L
FT4: FREE THYROXINE
Is the metabolically active thyroid hormone–not bound to protein
Should be ordered when TSH is abnormal to determine thyroid hyperfunction or
hypofunction
Normal range: 10 - 23 pmol/L
FT3: FREE TRIIODOTHYRONINE
In nonthyroidal illness, a low FT3 level is a nonspecific finding.
FT3 is done to rule out T3 toxicosis
Normal Adults: 4.0–7.4 pmol/L
FREE THYROXINE INDEX (FTI) The free thyroxine index (FTI) is a mathematical calculation
used to correct the estimated total T 4 for the amount of TBG present.
Make a calculation based on results of T 3 uptake and T 4 total, as follows: FTI= Total T4XT3 UPTAKE(%)/100
Normal Adults: 1.5–4.5 index
METHODS USED TO MEASURE THYROID HORMONES
• RadioimmunoassayRIA• Enzyme-linked immunosorbant
assayELISA• Chemiluminescent immunoassayCLIA• Fluorescent immunoassayFIA
THYROID ANTIBODIES
Antithyroid peroxidase antibodies
Used to diagnose suspected Hashimoto’s thyroiditis in
hypothyroidism
Antithyroglobulin antibodies
Used to diagnose autoimmune thyroiditis or Graves’ disease in
hyperthyroidism
TRH RESPONSE TESTTRH RESPONSE TEST
TRH administration stimulate production of TSH
If hypothalamo-pituitary-thyroid axis is normal, T3 and T4 secretions will be increased
TRH RESPONSE TESTIn primary
hyperthyroidism
• little or no change in TSH levels
In primary hypothyroidism
• Prompt
increase in TSH
In secondary hypothyroidism• Does not
produce an increase in TSH
RADIOACTIVE IODINE UPTAKE131I used to detect
functional derangements of
thyroid gland.About 15 mci of 131I given intravenousl
y After a few hours, the patient is monitored at the
neck region by movable gamma-ray counter, which will pick up the radiation emitted by thyroid
gland
RADIOACTIVE IODINE UPTAKE
Normal response• About 25% uptake by
thyroid within 2 hours• About 50% uptake by
thyroid within 24 hours
Abnormal response• Increased uptake in
hyperthyroidism• Decreased uptake in
hyporthyroidism