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

Step 1: Understanding the Question:
We need to identify which of these four causes of metabolic acidosis does NOT typically raise the anion gap.

Step 2: Key Formula or Approach:
The anion gap rises when acid accumulates in the form of an unmeasured anion, such as a ketone, lactate, or toxic metabolite, while it stays normal when the acidosis is instead caused by direct loss of bicarbonate, which gets replaced by chloride.

Step 3: Detailed Explanation:
Diabetic ketoacidosis raises the anion gap because ketone bodies, which are unmeasured anions, accumulate in the blood as bicarbonate is consumed.
Lactic acidosis raises the anion gap because lactate itself is an unmeasured anion that builds up as bicarbonate is consumed buffering the excess acid.
Methanol poisoning raises the anion gap because methanol is metabolized into formic acid, whose unmeasured anion accumulates in the blood.
Renal tubular acidosis is different because it is caused by the kidney's inability to properly reabsorb bicarbonate or excrete hydrogen ions, so bicarbonate is lost directly and replaced by chloride in the blood, keeping the anion gap normal even though the patient has metabolic acidosis. This is why renal tubular acidosis is classified as a normal anion gap, or hyperchloremic, metabolic acidosis.

Step 4: Final Answer:
So the condition that does NOT cause an increased anion gap metabolic acidosis is renal tubular acidosis, since it produces a normal anion gap, hyperchloremic acidosis instead.