Endocrinology: non-thyroidal illness: 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 · Endocrinology: non-thyroidal illness

Sample item

A 62-year-old man in intensive care with severe sepsis has a normal TSH, low total and free T3, low-normal T4 and a raised reverse T3. He has no thyroid disease. Which mechanism best explains this pattern?

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

The answer and the reasoning

A. Reduced peripheral conversion of T4 to T3, with T4 diverted to reverse T3

In severe systemic illness, cytokines and stress hormones reduce deiodinase activity, so less T4 is converted to active T3 and more goes to inactive reverse T3. TSH stays normal and the thyroid itself is healthy, so thyroid function tests are best repeated after recovery rather than treated.

Option by option

  • A. Reduced peripheral conversion of T4 to T3, with T4 diverted to reverse T3 (correct)

    Correct. Impaired outer-ring deiodination lowers T3 and raises reverse T3 while TSH remains normal.

  • B. Autoimmune destruction of follicular cells with failing T4 output

    Autoimmune destruction would cause low T4 with a raised TSH, and reverse T3 would not be raised.

  • C. Iodide excess blocking organification of iodine in the follicles

    Excess iodide would cause hypothyroidism with a raised TSH, and would not raise reverse T3 in this way.

  • D. Loss of thyrotroph function with absent TSH drive to the gland

    Thyrotroph failure would give a low or inappropriately low TSH with low T4, which is not the pattern seen.

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.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is A, Reduced peripheral conversion of T4 to T3, with T4 diverted to reverse T3. In severe systemic illness, cytokines and stress hormones reduce deiodinase activity, so less T4 is converted to active T3 and more goes to inactive reverse T3.

Why is "Autoimmune destruction of follicular cells with failing T4 output" not the answer?

Autoimmune destruction would cause low T4 with a raised TSH, and reverse T3 would not be raised.

Why is "Iodide excess blocking organification of iodine in the follicles" not the answer?

Excess iodide would cause hypothyroidism with a raised TSH, and would not raise reverse T3 in this way.

Why is "Loss of thyrotroph function with absent TSH drive to the gland" not the answer?

Thyrotroph failure would give a low or inappropriately low TSH with low T4, which is not the pattern seen.

What concept does this question test?

It tests Endocrinology: non-thyroidal illness in Physiology. TSH stays normal and the thyroid itself is healthy, so thyroid function tests are best repeated after recovery rather than treated.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Endocrinology: non-thyroidal illness?

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.