Haematology: vitamin B12 deficiency: practice question

A General Medicine 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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General Medicine · Haematology: vitamin B12 deficiency

Sample item

A 62-year-old strict vegetarian has macrocytic anaemia, paraesthesia and loss of vibration sense. Which biochemical result is expected?

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

The answer and the reasoning

B. Raised homocysteine and raised methylmalonic acid

Vitamin B12 is needed for converting methylmalonyl CoA to succinyl CoA and homocysteine to methionine, so both metabolites rise in deficiency. In folate deficiency only homocysteine rises. Neurological damage from B12 deficiency can be irreversible if untreated, and folate alone may worsen it.

Option by option

  • A. Both homocysteine and methylmalonic acid normal

    Normal values would exclude significant deficiency.

  • B. Raised homocysteine and raised methylmalonic acid (correct)

    Correct. B12 deficiency raises both metabolites.

  • C. Raised homocysteine with normal methylmalonic acid

    This pattern is typical of folate deficiency.

  • D. Normal homocysteine with raised methylmalonic acid

    Isolated methylmalonic acid elevation is not the usual B12 pattern.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is B, Raised homocysteine and raised methylmalonic acid. Vitamin B12 is needed for converting methylmalonyl CoA to succinyl CoA and homocysteine to methionine, so both metabolites rise in deficiency.

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

Normal values would exclude significant deficiency.

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

This pattern is typical of folate deficiency.

Why is "Normal homocysteine with raised methylmalonic acid" not the answer?

Isolated methylmalonic acid elevation is not the usual B12 pattern.

What concept does this question test?

It tests Haematology: vitamin B12 deficiency in General Medicine. In folate deficiency only homocysteine rises. Neurological damage from B12 deficiency can be irreversible if untreated, and folate alone may worsen 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 Haematology: vitamin B12 deficiency?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.