Clinical biochemistry: non-thyroidal illness: practice question

A Biochemistry 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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Biochemistry · Clinical biochemistry: non-thyroidal illness

Sample item

A septic patient on a ventilator has TSH 0.6 mIU/L, low free T3, low-normal free T4 and a raised reverse T3. There is no history of thyroid disease. What is the best interpretation?

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

The answer and the reasoning

D. Non-thyroidal illness with reduced T4 to T3 conversion

Severe illness inhibits peripheral deiodination of T4 to T3 and favours reverse T3 formation, so T3 falls while TSH stays near normal. Thyroid function should not be tested in acutely ill patients without suspicion, and no thyroxine is needed. Tests are repeated after recovery.

Option by option

  • A. Thyrotoxicosis factitia

    Factitious thyrotoxicosis would give a suppressed TSH with high free T4.

  • B. Primary hypothyroidism

    Primary hypothyroidism would have a raised TSH.

  • C. Graves disease

    Graves disease would give a suppressed TSH with high free hormones.

  • D. Non-thyroidal illness with reduced T4 to T3 conversion (correct)

    Correct. Low T3 with raised reverse T3 and unremarkable TSH fits the sick euthyroid pattern.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Non-thyroidal illness with reduced T4 to T3 conversion. Severe illness inhibits peripheral deiodination of T4 to T3 and favours reverse T3 formation, so T3 falls while TSH stays near normal.

Why is "Thyrotoxicosis factitia" not the answer?

Factitious thyrotoxicosis would give a suppressed TSH with high free T4.

Why is "Primary hypothyroidism" not the answer?

Primary hypothyroidism would have a raised TSH.

Why is "Graves disease" not the answer?

Graves disease would give a suppressed TSH with high free hormones.

What concept does this question test?

It tests Clinical biochemistry: non-thyroidal illness in Biochemistry. Thyroid function should not be tested in acutely ill patients without suspicion, and no thyroxine is needed. Tests are repeated after recovery.

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 Clinical biochemistry: non-thyroidal illness?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.