Which condition will cause an increased anion gap?

• A. Hypoaldosteronism
• B. Diarrhea
• C. Renal failure
• D. Hyperkalemia

Answer: (C)

An increased anion gap reflects accumulation of unmeasured anions in metabolic acidosis. When unmeasured acids such as lactate, ketones, sulfate, or phosphate build up, the gap between measured cations and anions widens.

Renal failure causes retention of these organic acids (uremic acidosis), leading to a higher anion gap. In contrast, diarrhea and hypoaldosteronism typically produce a hyperchloremic (normal anion gap) metabolic acidosis due to loss or retention of chloride and bicarbonate, not an accumulation of unmeasured anions. Hyperkalemia by itself does not raise the anion gap.

Therefore, renal failure is the condition that increases the anion gap.