Clinical biochemistry: D-lactic acidosis: 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: D-lactic acidosis

Sample item

A woman with short bowel after ileal resection has episodes of confusion, slurred speech and ataxia after carbohydrate-rich meals. She has a high anion gap acidosis, but serum lactate by the standard assay is normal. Urine ketones are negative and the osmolal gap is normal. What explains the acidosis?

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

The answer and the reasoning

C. Bacterial D-lactate not detected by the routine lactate assay

Unabsorbed carbohydrate reaching the colon is fermented by bacteria to D-lactate, which is absorbed and causes encephalopathy with a high anion gap acidosis. Standard lactate oxidase assays measure only L-lactate, so the value looks normal. Treatment is dietary carbohydrate restriction and antibiotics.

Option by option

  • A. Starvation ketoacidosis

    Ketones are negative in the urine.

  • B. Glycolic acid accumulation from ethylene glycol

    Ethylene glycol would raise the osmolal gap, which is normal.

  • C. Bacterial D-lactate not detected by the routine lactate assay (correct)

    Correct. D-lactate is made by gut bacteria and missed by the L-lactate-specific assay.

  • D. Salicylate toxicity

    Salicylate toxicity causes tinnitus and a mixed acid-base disorder, with no link to short bowel.

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 C, Bacterial D-lactate not detected by the routine lactate assay. Unabsorbed carbohydrate reaching the colon is fermented by bacteria to D-lactate, which is absorbed and causes encephalopathy with a high anion gap acidosis.

Why is "Starvation ketoacidosis" not the answer?

Ketones are negative in the urine.

Why is "Glycolic acid accumulation from ethylene glycol" not the answer?

Ethylene glycol would raise the osmolal gap, which is normal.

Why is "Salicylate toxicity" not the answer?

Salicylate toxicity causes tinnitus and a mixed acid-base disorder, with no link to short bowel.

What concept does this question test?

It tests Clinical biochemistry: D-lactic acidosis in Biochemistry. Standard lactate oxidase assays measure only L-lactate, so the value looks normal. Treatment is dietary carbohydrate restriction and antibiotics.

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: D-lactic acidosis?

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.