Clinical biochemistry: heterophilic antibody interference: 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: heterophilic antibody interference

Sample item

A woman has a persistently positive serum beta-hCG of 40 IU/L with no pregnancy on ultrasound. Urine hCG is negative, and the serum result does not fall in a linear way on serial dilution. What is the most likely explanation?

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

The answer and the reasoning

A. Heterophilic antibodies cross-linking the sandwich assay

Heterophilic antibodies bridge the capture and detection antibodies of a sandwich immunoassay and produce a false positive result. Because they are not filtered into urine, the urine test is negative, and dilution is non-linear. Testing on a different platform confirms it.

Option by option

  • A. Heterophilic antibodies cross-linking the sandwich assay (correct)

    Correct. Assay interference explains a positive serum test with a negative urine test and non-linear dilution.

  • B. Ectopic pregnancy

    Ectopic pregnancy would also give a positive urine test.

  • C. High-dose hook effect

    A hook effect lowers the reading in extreme excess and does not cause a false positive.

  • D. Choriocarcinoma

    Choriocarcinoma would give a rising value and positive urine test.

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 A, Heterophilic antibodies cross-linking the sandwich assay. Heterophilic antibodies bridge the capture and detection antibodies of a sandwich immunoassay and produce a false positive result.

Why is "Ectopic pregnancy" not the answer?

Ectopic pregnancy would also give a positive urine test.

Why is "High-dose hook effect" not the answer?

A hook effect lowers the reading in extreme excess and does not cause a false positive.

Why is "Choriocarcinoma" not the answer?

Choriocarcinoma would give a rising value and positive urine test.

What concept does this question test?

It tests Clinical biochemistry: heterophilic antibody interference in Biochemistry. Because they are not filtered into urine, the urine test is negative, and dilution is non-linear. Testing on a different platform confirms it.

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: heterophilic antibody interference?

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.