Vitamins: thiamine status assessment: 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 · Vitamins: thiamine status assessment

Sample item

A malnourished man with chronic alcohol use has tachycardia and peripheral oedema. Which laboratory test best demonstrates functional thiamine deficiency?

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

The answer and the reasoning

A. Erythrocyte transketolase activity with a marked increase after adding thiamine pyrophosphate

Transketolase of the pentose phosphate pathway requires thiamine pyrophosphate. In deficiency, red cell transketolase activity is low and rises sharply when the cofactor is added in vitro, the TPP effect. This is the classic functional assay for thiamine status.

Option by option

  • A. Erythrocyte transketolase activity with a marked increase after adding thiamine pyrophosphate (correct)

    A large TPP effect shows the apoenzyme is under-saturated with cofactor, indicating thiamine deficiency.

  • B. Erythrocyte glutathione reductase activity coefficient

    The glutathione reductase activity coefficient assesses riboflavin status.

  • C. Urinary methylmalonic acid

    Urinary methylmalonic acid is raised in vitamin B12 deficiency.

  • D. Urinary formiminoglutamate after a histidine load

    Formiminoglutamate excretion after histidine is raised in 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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, Erythrocyte transketolase activity with a marked increase after adding thiamine pyrophosphate. Transketolase of the pentose phosphate pathway requires thiamine pyrophosphate.

Why is "Erythrocyte glutathione reductase activity coefficient" not the answer?

The glutathione reductase activity coefficient assesses riboflavin status.

Why is "Urinary methylmalonic acid" not the answer?

Urinary methylmalonic acid is raised in vitamin B12 deficiency.

Why is "Urinary formiminoglutamate after a histidine load" not the answer?

Formiminoglutamate excretion after histidine is raised in folate deficiency.

What concept does this question test?

It tests Vitamins: thiamine status assessment in Biochemistry. In deficiency, red cell transketolase activity is low and rises sharply when the cofactor is added in vitro, the TPP effect. This is the classic functional assay for thiamine status.

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 Vitamins: thiamine status assessment?

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.