Severe diarrhea due to Clostridium difficile toxin is most commonly associated with which acid-base disorder?

• A. Metabolic alkalosis
• B. Respiratory alkalosis
• C. Metabolic acidosis
• D. Respiratory acidosis

Answer: (C)

Bicarbonate loss in severe diarrhea drives a metabolic acidosis. Gut fluids contain a lot of bicarbonate, and when they’re lost in large quantities through diarrhea, the body loses base faster than acid, lowering HCO3- and pH. This typically presents as a non-anion gap (hyperchloremic) metabolic acidosis, with the respiratory system compensating by increasing ventilation to lower CO2. In CDI, lactic acidosis from poor perfusion can add an elevated anion gap component if sepsis develops, but the classic pattern from diarrheal bicarbonate loss is metabolic acidosis. This is why metabolic acidosis is the best answer.