Vitamin metabolism: 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 · Vitamin metabolism

Sample item

Which laboratory abnormality is specifically associated with vitamin B12 deficiency rather than isolated folate deficiency?

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

The answer and the reasoning

C. Raised methylmalonic acid

Vitamin B12 is required for conversion of methylmalonyl-CoA to succinyl-CoA, so B12 deficiency raises methylmalonic acid, whereas isolated folate deficiency does not usually do so.

Option by option

  • A. Raised bilirubin

    Bilirubin may change in haemolysis but does not distinguish these vitamin deficiencies.

  • B. Raised LDL cholesterol

    LDL cholesterol is not the discriminating marker between B12 and folate deficiency.

  • C. Raised methylmalonic acid (correct)

    Correct: methylmalonic acid rises in B12 deficiency.

  • D. Low serum sodium

    Low sodium has many causes but is not the key B12 marker.

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 C, Raised methylmalonic acid. Vitamin B12 is required for conversion of methylmalonyl-CoA to succinyl-CoA, so B12 deficiency raises methylmalonic acid, whereas isolated folate deficiency does not usually do so.

Why is "Raised bilirubin" not the answer?

Bilirubin may change in haemolysis but does not distinguish these vitamin deficiencies.

Why is "Raised LDL cholesterol" not the answer?

LDL cholesterol is not the discriminating marker between B12 and folate deficiency.

Why is "Low serum sodium" not the answer?

Low sodium has many causes but is not the key B12 marker.

What concept does this question test?

It tests Vitamin metabolism in Biochemistry. The correct option holds because: Correct: methylmalonic acid rises in B12 deficiency.

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 Vitamin metabolism?

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.