Thyroid Function Tests - QS Study
QS Study

Thyroid hormones are two hormones produced and released by the thyroid gland, namely triiodothyronine (T3) and thyroxine (T4). They act to increase the basal metabolic rate, affect protein synthesis, help regulate long bone growth and neural maturation, and increase the body’s sensitivity to catecholamines by permissiveness.

Thyroid Function Tests – These tests are a series of blood tests used to measure how well your thyroid gland is working.

(A) Measurement of plasma conc. TSH by RIA (Radioimmune assay)

(B) Measurement of plasma conc. of T3 and T4 (free) TSH and total T4.

(C) Thyroid scanning: Determination of uptake of radioactive iodine (I131) by the thyroid gland. Its principal value is in the toxic patient with nodule or nodularity of the thyroid.

(D) Measurement of plasma conc. of TSI by RIA. (Radio Immune Assay)

(E) Determination of blood cholesterol level;

  • Normal: 150 – 300 mg %.
  • In hyperthyroidism: < 150 mg %.
  • In hypothyroidism: > 300 mg %.

(F) Determination of butanol extractable iodine test:

  • Normal: 2 – 6 μgm/100 dl
  • In hypothyroidism < 2 μg/100 dl
  • In hyperthyroidism > 6 μg/100 dl.

(G) Determination of protein-bound iodine.

  • Normal: 4-8 μgm,
  • Hypothyroidism: < 4 μgm,
  • Hyperthyroidism > 8 μgm.

(H) Determination of BMR:

  • In normal: 40 cal/m2 of surface area,
  • In Hyperthyroidism: 50% above normal,
  • In Hypothyroidism: 30-40% below normal.

Characteristic of Thyroid function test in Common Thyroid Disorder –

Determination of Radioactive Iodine uptake (I131) by the thyroid gland

Procedure: The patient is given a small dose of radioactive (I131) iodine which accumulates for the thyroid gland and estimates in a different time interval.

Significance: It is done to detect the hyperthyroidism.

  • Normal value: 0.75 μgm/day,
  • In hypothyroidism: 20% below normal,
  • In hyperthyroidism: 40% above normal.