Tumour markers: free PSA: 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 · Tumour markers: free PSA

Sample item

A 66-year-old man has a total PSA of 7 ng/mL with a normal rectal examination. The free to total PSA ratio is 8%. How is this interpreted?

AA low ratio favours benign prostatic hyperplasiaBA low ratio proves prostatitisCA low ratio favours carcinoma, because PSA in cancer is mostly bound to alpha-1 antichymotrypsinDThe ratio has no relevance because total PSA is below 10

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

The answer and the reasoning

C. A low ratio favours carcinoma, because PSA in cancer is mostly bound to alpha-1 antichymotrypsin

In the 4 to 10 ng/mL range, a low percentage of free PSA (about 10% or less carries a high risk, whereas above about 25% is reassuring) raises the probability of carcinoma, because PSA from cancer is released in complexed form while BPH gives relatively more free PSA. It is a risk stratifier, and biopsy or MRI decides the diagnosis. PSA is organ specific but not cancer specific.

Option by option

A. A low ratio favours benign prostatic hyperplasia
BPH is associated with a higher free fraction.
B. A low ratio proves prostatitis
Prostatitis raises total PSA but a ratio cannot prove it.
C. A low ratio favours carcinoma, because PSA in cancer is mostly bound to alpha-1 antichymotrypsin (correct)
Correct. A smaller free fraction indicates more complexed PSA, as seen in cancer.
D. The ratio has no relevance because total PSA is below 10
The ratio is most useful precisely in the intermediate range.

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 C, A low ratio favours carcinoma, because PSA in cancer is mostly bound to alpha-1 antichymotrypsin. In the 4 to 10 ng/mL range, a low percentage of free PSA (about 10% or less carries a high risk, whereas above about 25% is reassuring) raises the probability of carcinoma, because PSA from cancer is released in complexed form while BPH gives relatively more free PSA.

Why is "A low ratio favours benign prostatic hyperplasia" not the answer?

BPH is associated with a higher free fraction.

Why is "A low ratio proves prostatitis" not the answer?

Prostatitis raises total PSA but a ratio cannot prove it.

Why is "The ratio has no relevance because total PSA is below 10" not the answer?

The ratio is most useful precisely in the intermediate range.

What concept does this question test?

It tests Tumour markers: free PSA in Biochemistry. It is a risk stratifier, and biopsy or MRI decides the diagnosis. PSA is organ specific but not cancer specific.

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 Tumour markers: free PSA?

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.