Endocrinology: cortisol rhythm: 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: cortisol rhythm

Sample item

A 35-year-old woman with weight gain and striae is being screened for Cushing syndrome. Which test best uses the normal physiology of cortisol secretion?

ALate-night salivary cortisol, because the normal midnight nadir is lostBSerum cortisol at 8 am, because it is the daily peakCSerum cortisol at noon, because it is the most stable valueDUrinary sodium excretion, because cortisol lowers it

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

The answer and the reasoning

A. Late-night salivary cortisol, because the normal midnight nadir is lost

Cortisol follows a diurnal rhythm driven by CRH and ACTH, peaking in the early morning and reaching a nadir around midnight. In Cushing syndrome the nadir is lost, so a raised late-night salivary or serum cortisol is a sensitive screening test. Morning values overlap with normal and are not useful.

Option by option

A. Late-night salivary cortisol, because the normal midnight nadir is lost (correct)
Correct. Absence of the midnight nadir is a hallmark of endogenous hypercortisolism.
B. Serum cortisol at 8 am, because it is the daily peak
Morning values are physiologically high and do not discriminate.
C. Serum cortisol at noon, because it is the most stable value
Noon values do not exploit the loss of rhythm.
D. Urinary sodium excretion, because cortisol lowers it
Urinary sodium is not a recognised screening test for Cushing syndrome.

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 A, Late-night salivary cortisol, because the normal midnight nadir is lost. Cortisol follows a diurnal rhythm driven by CRH and ACTH, peaking in the early morning and reaching a nadir around midnight.

Why is "Serum cortisol at 8 am, because it is the daily peak" not the answer?

Morning values are physiologically high and do not discriminate.

Why is "Serum cortisol at noon, because it is the most stable value" not the answer?

Noon values do not exploit the loss of rhythm.

Why is "Urinary sodium excretion, because cortisol lowers it" not the answer?

Urinary sodium is not a recognised screening test for Cushing syndrome.

What concept does this question test?

It tests Endocrinology: cortisol rhythm in Physiology. In Cushing syndrome the nadir is lost, so a raised late-night salivary or serum cortisol is a sensitive screening test. Morning values overlap with normal and are not useful.

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: cortisol rhythm?

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.