Clinical biochemistry: glycated haemoglobin: 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: glycated haemoglobin

Sample item

A man with type 2 diabetes and chronic haemolytic anaemia has an HbA1c of 5.2% while his home glucose readings are consistently above 250 mg/dL. What is the most likely reason for the discrepancy?

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

The answer and the reasoning

C. Shortened red cell lifespan reduces the time haemoglobin is exposed to glucose, so HbA1c falsely underestimates control

HbA1c reflects average glycaemia over the lifespan of red cells, around 2 to 3 months. Conditions that shorten red cell survival (haemolysis, recent blood loss or transfusion) lower HbA1c falsely. In such cases fructosamine or glucose monitoring give a more reliable picture.

Option by option

  • A. Haemolysis increases glycation of haemoglobin

    Reduced exposure time lowers glycation rather than raising it.

  • B. HbA1c measures glucose over the previous 24 hours only

    HbA1c reflects the preceding 2 to 3 months, not 24 hours.

  • C. Shortened red cell lifespan reduces the time haemoglobin is exposed to glucose, so HbA1c falsely underestimates control (correct)

    Correct. Younger red cells have had less exposure to glucose, so HbA1c reads low.

  • D. HbA1c does not reflect glucose in diabetes

    HbA1c does reflect glycaemia in diabetes but is unreliable when red cell survival is abnormal.

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, Shortened red cell lifespan reduces the time haemoglobin is exposed to glucose, so HbA1c falsely underestimates control. HbA1c reflects average glycaemia over the lifespan of red cells, around 2 to 3 months.

Why is "Haemolysis increases glycation of haemoglobin" not the answer?

Reduced exposure time lowers glycation rather than raising it.

Why is "HbA1c measures glucose over the previous 24 hours only" not the answer?

HbA1c reflects the preceding 2 to 3 months, not 24 hours.

Why is "HbA1c does not reflect glucose in diabetes" not the answer?

HbA1c does reflect glycaemia in diabetes but is unreliable when red cell survival is abnormal.

What concept does this question test?

It tests Clinical biochemistry: glycated haemoglobin in Biochemistry. Conditions that shorten red cell survival (haemolysis, recent blood loss or transfusion) lower HbA1c falsely. In such cases fructosamine or glucose monitoring give a more reliable picture.

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 Clinical biochemistry: glycated haemoglobin?

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.