Question:medium
All of the following cause high anion gap metabolic acidosis except:
All of the following cause high anion gap metabolic acidosis except:
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Ureterosigmoidostomy causes chloride gain and bicarbonate loss, so the gap stays normal.
Updated On: Jul 8, 2026
- Lactic acidosis.
- Salicylate poisoning.
- Ethylene glycol poisoning.
- Ureterosigmoidostomy.
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The Correct Option is D
Solution and Explanation
Concept:
Metabolic acidosis splits into two groups based on the anion gap: high gap, where an unmeasured acid appears, and normal gap, where bicarbonate is lost directly and chloride rises to compensate.
Step 1: Check the classic acid producing causes.
Lactic acid built up during poor tissue oxygenation is an unmeasured acid. Salicylate overdose releases organic acids. Ethylene glycol is broken down in the liver into glycolic and oxalic acids. All three add an unmeasured acid to the blood, so all three widen the anion gap.
Step 2: Check ureterosigmoidostomy.
After this surgery, urine sits in the colon, and the colon wall swaps chloride from the urine for bicarbonate, which then leaves the body in stool. The net effect is bicarbonate loss matched by chloride gain, not the appearance of a new unmeasured acid.
Step 3: Compare the two mechanisms.
Since chloride rises as bicarbonate falls, sodium minus (chloride plus bicarbonate) stays about the same, so the anion gap stays normal here, unlike the other three causes.
Step 4: Conclude.
The one that does not raise the anion gap is ureterosigmoidostomy.
\[ \boxed{\text{Ureterosigmoidostomy}} \]
Metabolic acidosis splits into two groups based on the anion gap: high gap, where an unmeasured acid appears, and normal gap, where bicarbonate is lost directly and chloride rises to compensate.
Step 1: Check the classic acid producing causes.
Lactic acid built up during poor tissue oxygenation is an unmeasured acid. Salicylate overdose releases organic acids. Ethylene glycol is broken down in the liver into glycolic and oxalic acids. All three add an unmeasured acid to the blood, so all three widen the anion gap.
Step 2: Check ureterosigmoidostomy.
After this surgery, urine sits in the colon, and the colon wall swaps chloride from the urine for bicarbonate, which then leaves the body in stool. The net effect is bicarbonate loss matched by chloride gain, not the appearance of a new unmeasured acid.
Step 3: Compare the two mechanisms.
Since chloride rises as bicarbonate falls, sodium minus (chloride plus bicarbonate) stays about the same, so the anion gap stays normal here, unlike the other three causes.
Step 4: Conclude.
The one that does not raise the anion gap is ureterosigmoidostomy.
\[ \boxed{\text{Ureterosigmoidostomy}} \]
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