A chronic alcoholic presents after 3 days of vomiting with abdominal pain, tachypnea, and a normal glucose level. Serum beta-hydroxybutyrate is markedly elevated, but the bedside nitroprusside (Acetest) reaction is only weakly positive. The most likely explanation for this discrepancy is:
- A Nitroprusside requires the presence of free fatty acids to generate a color change
- B Alcoholic ketoacidosis produces acetone exclusively, which nitroprusside fails to detect
- C Nitroprusside reacts only with acetoacetate, which is reduced to beta-hydroxybutyrate when hepatic NADH is high ✓
- D Beta-hydroxybutyrate is excreted rapidly in urine, lowering its serum detectability
Correct answer: C. Nitroprusside reacts only with acetoacetate, which is reduced to beta-hydroxybutyrate when hepatic NADH is high
Explanation
The nitroprusside test detects only acetoacetate, not beta-hydroxybutyrate. Ethanol metabolism raises the hepatic NADH:NAD+ ratio, driving mitochondrial dehydrogenases to reduce acetoacetate to beta-hydroxybutyrate, so total ketosis is severe while the test reads falsely mild. Option A is wrong because nitroprusside reacts directly with acetoacetate and acetone, independent of fatty acids. This explains why direct enzymatic measurement of beta-hydroxybutyrate is preferred in suspected alcoholic ketoacidosis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.