Answers to Review Questions in Thyroid Function and Abnormalities

1.    How are T3 and T4 formed?

T3 is formed from the combination of 1 diidothyronine and 1 monoiodothyronine, while T4 is formed by the combination of 2 diiodothyronine molecules.

2.    What's more biologically active between T3 and T4?

Although total T4 is more elevated in the blood stream, T3 is more biologically active because it has more free forms than T3. The free forms are responsible for the activity of the hormone in the body.

3.    What would be a more reliable test between T3 and T4 to test Thyroid Function?

Both can be performed, including TSH to determine thyroid function.

4.    What other tests can be performed for TFT (Thyroid Function Test)?

TSH test and T3 uptake test. Also, FT3, FT4.

5.    What abnormalities can result from insufficient or elevated T3 and T4?

Hyperthyroidism – elevated T3 and T4; decreased TSH
Hypothyroidism – low T3 and T4; increased TSH

Thyroid Function Test, Case Analysis

CASE ANALYSIS 4

•      AN APPARENTLY HEALTHY 33 YR-OLD WOMAN UNDERGOES THYROID TESTING WITH THE FOLLOWING RESULTS:  FT4 = 1.2 ng/dL, s-TSH = 15 uU/mL.  NO GOITER OR ANY OTHER ABNORMALITY IS NOTED.  THE PHYSICIAN IS CONCERNED, BUT DECIDES TO FOLLOW THE PATIENT FOR EVERY SIX MONTHS.  SIX MONTHS LATER THE PATIENT’S FT4= 1.1 ng/dL, s –TSH = 25 uU/mL.

QUESTIONS

•      1.  WHAT CLINICAL STATE IS THE PATIENT APPARENTLY EXHIBITING? DEFEND YOUR ANSWER?

•      2.  WHY IS THERE CONCERN OVER THESE RESULTS?

•      3.  WHY WOULD MOST LABORATORY THYROID TESTS NOT BE USEFUL IN THIS CASE?

•      4.  WHAT LABORATORY TEST WOULD BE USEFUL? WHY?

CHECK ANSWERS HERE