Question

Metabolic acidosis with increased anion gap occurs in all of the following EXCEPT

• A. Diabetic keto acidosis
• B. Lactic acidosis
• C. Renal tubular acidosis
• D. Methanol poisoning

Hint:

Look for the cause where bicarbonate loss is replaced by chloride rather than by an unmeasured acid anion.

Answer 1

The Correct Option is C

This question asks which of four causes of metabolic acidosis is the exception that does not raise the anion gap.

1. Diabetic keto acidosis: Accumulating ketone bodies are unmeasured anions that raise the anion gap.
2. Lactic acidosis: Lactate itself is an unmeasured anion, so it raises the anion gap as it accumulates.
3. Renal tubular acidosis: Here bicarbonate is lost directly through the kidney and replaced by chloride, so the anion gap stays normal even though the patient is acidotic. This is the classic normal anion gap, hyperchloremic type of metabolic acidosis.
4. Methanol poisoning: Methanol is converted to formic acid, whose unmeasured anion raises the anion gap.

Since renal tubular acidosis replaces lost bicarbonate with chloride rather than an unmeasured anion, it is the exception that keeps the anion gap normal.

Let's summarize:

• DKA, lactic acidosis, and methanol poisoning all add an unmeasured acid anion, raising the anion gap.
• Renal tubular acidosis instead loses bicarbonate and gains chloride, keeping the anion gap normal.

So the exception is renal tubular acidosis.