Haematology: folate versus vitamin B12 deficiency: practice question

A Pathology 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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Pathology · Haematology: folate versus vitamin B12 deficiency

Sample item

A 30-year-old woman with chronic alcohol use has macrocytic anaemia and hypersegmented neutrophils. She has no neurological signs. Serum folate is low and vitamin B12 is normal. Which pattern of metabolites is expected?

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

The answer and the reasoning

D. Raised homocysteine with normal methylmalonic acid

Folate is needed to remethylate homocysteine to methionine, so deficiency raises homocysteine. Methylmalonic acid is raised in vitamin B12 deficiency but not in folate deficiency, because methylmalonyl-CoA mutase needs adenosylcobalamin. This distinction matters because giving folic acid alone to a B12-deficient patient can correct the anaemia while subacute combined degeneration progresses.

Option by option

  • A. Raised methylmalonic acid with normal homocysteine

    Raised methylmalonic acid indicates vitamin B12 deficiency, which is excluded by the normal B12 level, and homocysteine is also usually raised in that state.

  • B. Normal homocysteine and normal methylmalonic acid

    Normal values would argue against a deficiency state, which this patient has.

  • C. Raised homocysteine and raised methylmalonic acid

    Both metabolites are raised in vitamin B12 deficiency and not in isolated folate deficiency.

  • D. Raised homocysteine with normal methylmalonic acid (correct)

    Isolated homocysteine elevation with normal methylmalonic acid points to folate deficiency.

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 Pathology question

What is the answer to this Pathology question?

The best answer is D, Raised homocysteine with normal methylmalonic acid. Folate is needed to remethylate homocysteine to methionine, so deficiency raises homocysteine.

Why is "Raised methylmalonic acid with normal homocysteine" not the answer?

Raised methylmalonic acid indicates vitamin B12 deficiency, which is excluded by the normal B12 level, and homocysteine is also usually raised in that state.

Why is "Normal homocysteine and normal methylmalonic acid" not the answer?

Normal values would argue against a deficiency state, which this patient has.

Why is "Raised homocysteine and raised methylmalonic acid" not the answer?

Both metabolites are raised in vitamin B12 deficiency and not in isolated folate deficiency.

What concept does this question test?

It tests Haematology: folate versus vitamin B12 deficiency in Pathology. Methylmalonic acid is raised in vitamin B12 deficiency but not in folate deficiency, because methylmalonyl-CoA mutase needs adenosylcobalamin. This distinction matters because giving folic acid alone to a B12-deficient patient can correct the anaemia while subacute combined degeneration progresses.

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 Haematology: folate versus vitamin B12 deficiency?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.