Blood and immunity: red cell oxidant defence: practice question

A Physiology 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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Physiology · Blood and immunity: red cell oxidant defence

Sample item

A 25-year-old man develops dark urine and jaundice two days after starting primaquine. His smear shows bite cells, and supravital staining shows blue-purple inclusions attached to the membrane. Which defect makes his red cells vulnerable?

ADeficient spectrin, causing loss of the biconcave shapeBInadequate ATP from glycolysis, causing failure of the cation pumpsCUnpaired globin chains precipitating within the red cellDToo little NADPH to keep glutathione reduced, so haemoglobin is oxidised

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

The answer and the reasoning

D. Too little NADPH to keep glutathione reduced, so haemoglobin is oxidised

Red cells depend on the pentose phosphate pathway for NADPH, which regenerates reduced glutathione to detoxify peroxides. When the first enzyme is deficient, oxidant drugs denature haemoglobin into Heinz bodies and macrophages remove the damaged cells, giving bite cells and haemolysis.

Option by option

A. Deficient spectrin, causing loss of the biconcave shape
Spectrin deficiency causes spherocytosis, with spherocytes rather than bite cells.
B. Inadequate ATP from glycolysis, causing failure of the cation pumps
ATP deficiency from pyruvate kinase loss gives chronic haemolysis, not drug-triggered episodes.
C. Unpaired globin chains precipitating within the red cell
Unpaired globin chains characterise thalassaemia and do not give an oxidant-triggered crisis.
D. Too little NADPH to keep glutathione reduced, so haemoglobin is oxidised (correct)
Correct. Without NADPH, glutathione cannot be regenerated and oxidant stress denatures haemoglobin.

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 Physiology question

What is the answer to this Physiology question?

The best answer is D, Too little NADPH to keep glutathione reduced, so haemoglobin is oxidised. Red cells depend on the pentose phosphate pathway for NADPH, which regenerates reduced glutathione to detoxify peroxides.

Why is "Deficient spectrin, causing loss of the biconcave shape" not the answer?

Spectrin deficiency causes spherocytosis, with spherocytes rather than bite cells.

Why is "Inadequate ATP from glycolysis, causing failure of the cation pumps" not the answer?

ATP deficiency from pyruvate kinase loss gives chronic haemolysis, not drug-triggered episodes.

Why is "Unpaired globin chains precipitating within the red cell" not the answer?

Unpaired globin chains characterise thalassaemia and do not give an oxidant-triggered crisis.

What concept does this question test?

It tests Blood and immunity: red cell oxidant defence in Physiology. When the first enzyme is deficient, oxidant drugs denature haemoglobin into Heinz bodies and macrophages remove the damaged cells, giving bite cells and haemolysis.

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 Blood and immunity: red cell oxidant defence?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.