Ketone bodies: urine nitroprusside test in DKA: 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 · Ketone bodies: urine nitroprusside test in DKA

Sample item

A 16-year-old girl with type 1 diabetes is brought with vomiting, Kussmaul breathing, glucose 480 mg/dL and an anion gap acidosis. A urine dipstick using sodium nitroprusside shows only a trace to 1+ ketone reaction. What best explains this?

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

The answer and the reasoning

D. Beta-hydroxybutyrate predominates because of a high NADH/NAD+ ratio, and the nitroprusside reaction does not detect it

In severe ketoacidosis the mitochondrial redox state is highly reduced, so acetoacetate is converted to beta-hydroxybutyrate, which can outnumber acetoacetate several fold. Nitroprusside reacts with acetoacetate (and weakly with acetone) but not with beta-hydroxybutyrate, so the test can underestimate ketosis. Serum beta-hydroxybutyrate measurement is more reliable.

Option by option

  • A. Acetoacetate is converted to glucose in the kidney, so very little is excreted

    Acetoacetate is not converted to glucose by the kidney, and ketone bodies are excreted in urine.

  • B. The nitroprusside test detects only acetone, which is volatile and exhaled

    Nitroprusside reacts mainly with acetoacetate, and acetone is only a weak reactant.

  • C. Ketone bodies are not produced in type 1 diabetes, so the acidosis is purely lactic

    Insulin deficiency increases hepatic ketogenesis, so the acidosis is from ketoacids.

  • D. Beta-hydroxybutyrate predominates because of a high NADH/NAD+ ratio, and the nitroprusside reaction does not detect it (correct)

    A reduced redox state favours beta-hydroxybutyrate, which the dipstick cannot detect.

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 D, Beta-hydroxybutyrate predominates because of a high NADH/NAD+ ratio, and the nitroprusside reaction does not detect it. In severe ketoacidosis the mitochondrial redox state is highly reduced, so acetoacetate is converted to beta-hydroxybutyrate, which can outnumber acetoacetate several fold.

Why is "Acetoacetate is converted to glucose in the kidney, so very little is…" not the answer?

Acetoacetate is not converted to glucose by the kidney, and ketone bodies are excreted in urine.

Why is "The nitroprusside test detects only acetone, which is volatile and ex…" not the answer?

Nitroprusside reacts mainly with acetoacetate, and acetone is only a weak reactant.

Why is "Ketone bodies are not produced in type 1 diabetes, so the acidosis is…" not the answer?

Insulin deficiency increases hepatic ketogenesis, so the acidosis is from ketoacids.

What concept does this question test?

It tests Ketone bodies: urine nitroprusside test in DKA in Biochemistry. Nitroprusside reacts with acetoacetate (and weakly with acetone) but not with beta-hydroxybutyrate, so the test can underestimate ketosis. Serum beta-hydroxybutyrate measurement is more reliable.

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 Ketone bodies: urine nitroprusside test in DKA?

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.