Endocrine: thyroid hormone binding: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Endocrine: thyroid hormone binding

Sample item

A woman at 10 weeks of gestation has total T4 above the normal range, but normal TSH and free T4, and no symptoms. What is the explanation?

AReduced renal clearance of free T4BReduced hepatic conversion of T4 to T3CAutonomous thyroid hormone secretion with TSH escapeDOestrogen raises thyroxine-binding globulin, increasing total but not free hormone

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Oestrogen raises thyroxine-binding globulin, increasing total but not free hormone

Oestrogen increases hepatic synthesis and sialylation of TBG, which raises the bound pool and total T4 and T3. Feedback maintains the free hormone concentration, and TSH stays normal, so she is euthyroid. Management is reassurance and using free hormone assays.

Option by option

A. Reduced renal clearance of free T4
Free T4 is normal, so there is no disorder of clearance.
B. Reduced hepatic conversion of T4 to T3
Conversion changes would alter T3 more than total T4 and would not explain the binding.
C. Autonomous thyroid hormone secretion with TSH escape
Autonomous secretion would give raised free T4 and suppressed TSH.
D. Oestrogen raises thyroxine-binding globulin, increasing total but not free hormone (correct)
Correct. The binding protein rises, so total hormone rises while free hormone is unchanged.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, Oestrogen raises thyroxine-binding globulin, increasing total but not free hormone. Oestrogen increases hepatic synthesis and sialylation of TBG, which raises the bound pool and total T4 and T3.

Why is "Reduced renal clearance of free T4" not the answer?

Free T4 is normal, so there is no disorder of clearance.

Why is "Reduced hepatic conversion of T4 to T3" not the answer?

Conversion changes would alter T3 more than total T4 and would not explain the binding.

Why is "Autonomous thyroid hormone secretion with TSH escape" not the answer?

Autonomous secretion would give raised free T4 and suppressed TSH.

What concept does this question test?

It tests Endocrine: thyroid hormone binding in Physiology. Feedback maintains the free hormone concentration, and TSH stays normal, so she is euthyroid. Management is reassurance and using free hormone assays.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Endocrine: thyroid hormone binding?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.