Haematology: isoniazid-induced sideroblastic anaemia: practice question

A Pathology 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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Pathology · Haematology: isoniazid-induced sideroblastic anaemia

Sample item

A 40-year-old man on antituberculosis treatment develops fatigue. Haemoglobin is 8 g/dL with a microcytic hypochromic picture. Serum iron and ferritin are high, and a marrow stained with Prussian blue shows ring sideroblasts. What is the most appropriate management?

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

The answer and the reasoning

B. Add pyridoxine to the regimen

Isoniazid antagonises pyridoxine (vitamin B6), the cofactor of ALA synthase in the first step of haem synthesis, so iron accumulates in mitochondria around the nucleus as ring sideroblasts. Pyridoxine supplementation corrects the anaemia and also protects against isoniazid neuropathy. Iron is contraindicated because stores are already high.

Option by option

  • A. Give parenteral cyanocobalamin

    Vitamin B12 treats macrocytic megaloblastic anaemia and is not the problem here.

  • B. Add pyridoxine to the regimen (correct)

    Pyridoxine restores ALA synthase activity and corrects the haem synthesis defect.

  • C. Start folic acid and stop all antituberculosis drugs

    Folic acid does not treat sideroblastic anaemia, and stopping all treatment is unnecessary and dangerous for tuberculosis.

  • D. Start oral iron supplementation

    Oral iron would add to the iron overload, since ferritin and serum iron are already high.

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 Pathology question

What is the answer to this Pathology question?

The best answer is B, Add pyridoxine to the regimen. Isoniazid antagonises pyridoxine (vitamin B6), the cofactor of ALA synthase in the first step of haem synthesis, so iron accumulates in mitochondria around the nucleus as ring sideroblasts.

Why is "Give parenteral cyanocobalamin" not the answer?

Vitamin B12 treats macrocytic megaloblastic anaemia and is not the problem here.

Why is "Start folic acid and stop all antituberculosis drugs" not the answer?

Folic acid does not treat sideroblastic anaemia, and stopping all treatment is unnecessary and dangerous for tuberculosis.

Why is "Start oral iron supplementation" not the answer?

Oral iron would add to the iron overload, since ferritin and serum iron are already high.

What concept does this question test?

It tests Haematology: isoniazid-induced sideroblastic anaemia in Pathology. Pyridoxine supplementation corrects the anaemia and also protects against isoniazid neuropathy. Iron is contraindicated because stores are already high.

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: isoniazid-induced sideroblastic anaemia?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.