Endocrinology: TSH as a screening test: 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: TSH as a screening test

Sample item

In suspected primary hypothyroidism, a serum TSH is preferred to a free T4 as the first screening test. Which relationship supports this?

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

The answer and the reasoning

B. A small fall in free T4 produces a large rise in TSH

The relationship between free T4 and TSH is log-linear and inverse. A two-fold change in free T4 can cause roughly a hundred-fold change in TSH, so TSH detects early or subclinical thyroid failure.

Option by option

  • A. TSH rises in direct proportion to free T4

    The relationship is inverse, not direct, because T4 suppresses TSH.

  • B. A small fall in free T4 produces a large rise in TSH (correct)

    Correct. The inverse log-linear relation amplifies small changes in free T4 into large changes in TSH.

  • C. TSH is unaffected until free T4 is below the normal range

    TSH starts rising while free T4 is still within the reference range, which is why it detects subclinical disease.

  • D. TSH has a longer half-life than T4

    T4 has a half-life of about a week, far longer than that of TSH.

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 B, A small fall in free T4 produces a large rise in TSH. The relationship between free T4 and TSH is log-linear and inverse.

Why is "TSH rises in direct proportion to free T4" not the answer?

The relationship is inverse, not direct, because T4 suppresses TSH.

Why is "TSH is unaffected until free T4 is below the normal range" not the answer?

TSH starts rising while free T4 is still within the reference range, which is why it detects subclinical disease.

Why is "TSH has a longer half-life than T4" not the answer?

T4 has a half-life of about a week, far longer than that of TSH.

What concept does this question test?

It tests Endocrinology: TSH as a screening test in Physiology. A two-fold change in free T4 can cause roughly a hundred-fold change in TSH, so TSH detects early or subclinical thyroid failure.

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 Endocrinology: TSH as a screening test?

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.