Clinical biochemistry: macroprolactin: 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: macroprolactin

Sample item

A woman with oligomenorrhoea has serum prolactin 90 ng/mL, a normal pituitary MRI and no galactorrhoea. After precipitation with polyethylene glycol, the prolactin falls to normal. Which explanation fits?

AHook effect from extreme prolactin excessBMacroprolactin, an immunoglobulin-bound complex with low bioactivityCProlactin-secreting macroadenomaDLoss of dopamine inhibition from stalk compression

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

The answer and the reasoning

B. Macroprolactin, an immunoglobulin-bound complex with low bioactivity

Macroprolactin is prolactin complexed to IgG, cleared slowly and detected by the assay although it is largely inactive. Polyethylene glycol precipitates the complex and the recovered level is normal. Recognising it prevents unnecessary imaging and dopamine agonist therapy.

Option by option

A. Hook effect from extreme prolactin excess
A hook effect gives falsely low values in very high prolactin, and dilution unmasks it.
B. Macroprolactin, an immunoglobulin-bound complex with low bioactivity (correct)
Correct. A complex precipitated by polyethylene glycol is macroprolactin.
C. Prolactin-secreting macroadenoma
A macroadenoma would be seen on MRI and the prolactin would not fall with precipitation.
D. Loss of dopamine inhibition from stalk compression
Stalk compression would show a mass on imaging.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Macroprolactin, an immunoglobulin-bound complex with low bioactivity. Macroprolactin is prolactin complexed to IgG, cleared slowly and detected by the assay although it is largely inactive.

Why is "Hook effect from extreme prolactin excess" not the answer?

A hook effect gives falsely low values in very high prolactin, and dilution unmasks it.

Why is "Prolactin-secreting macroadenoma" not the answer?

A macroadenoma would be seen on MRI and the prolactin would not fall with precipitation.

Why is "Loss of dopamine inhibition from stalk compression" not the answer?

Stalk compression would show a mass on imaging.

What concept does this question test?

It tests Clinical biochemistry: macroprolactin in Biochemistry. Polyethylene glycol precipitates the complex and the recovered level is normal. Recognising it prevents unnecessary imaging and dopamine agonist therapy.

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 Clinical biochemistry: macroprolactin?

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.