Clinical biochemistry: coeliac serology with IgA deficiency: 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: coeliac serology with IgA deficiency

Sample item

A 28-year-old woman with chronic diarrhoea and iron deficiency has a negative IgA anti-tissue transglutaminase result, but total serum IgA is markedly low. What is the best next step?

AMeasure faecal elastase to assess pancreatic functionBTest IgG-based tissue transglutaminase or deamidated gliadin antibodiesCConclude coeliac disease is excluded and stop further testingDRepeat IgA testing after six weeks on a gluten-free diet

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

The answer and the reasoning

B. Test IgG-based tissue transglutaminase or deamidated gliadin antibodies

IgA anti-tTG is the first-line serological test, but in selective IgA deficiency it can be falsely negative. IgG-based tTG or deamidated gliadin peptide antibodies should then be used. Testing must be done while the patient is eating gluten, and biopsy confirms the diagnosis.

Option by option

A. Measure faecal elastase to assess pancreatic function
Faecal elastase assesses pancreatic insufficiency and does not address the question.
B. Test IgG-based tissue transglutaminase or deamidated gliadin antibodies (correct)
Correct. IgG-based assays avoid the false negative caused by IgA deficiency.
C. Conclude coeliac disease is excluded and stop further testing
A negative IgA result is unreliable when IgA is deficient, so coeliac disease is not excluded.
D. Repeat IgA testing after six weeks on a gluten-free diet
A gluten-free diet lowers antibody levels and would make results falsely negative.

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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Test IgG-based tissue transglutaminase or deamidated gliadin antibodies. IgA anti-tTG is the first-line serological test, but in selective IgA deficiency it can be falsely negative.

Why is "Measure faecal elastase to assess pancreatic function" not the answer?

Faecal elastase assesses pancreatic insufficiency and does not address the question.

Why is "Conclude coeliac disease is excluded and stop further testing" not the answer?

A negative IgA result is unreliable when IgA is deficient, so coeliac disease is not excluded.

Why is "Repeat IgA testing after six weeks on a gluten-free diet" not the answer?

A gluten-free diet lowers antibody levels and would make results falsely negative.

What concept does this question test?

It tests Clinical biochemistry: coeliac serology with IgA deficiency in Biochemistry. IgG-based tTG or deamidated gliadin peptide antibodies should then be used. Testing must be done while the patient is eating gluten, and biopsy confirms the diagnosis.

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 Clinical biochemistry: coeliac serology with IgA deficiency?

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.