Which of the following is a cause of metabolic alkalosis?

• A. Late stage of salicylate poisoning
• B. Uncontrolled diabetes mellitus
• C. Renal failure
• D. Excessive vomiting

Answer: (D)

Metabolic alkalosis happens when there’s a net loss of hydrogen ions or a gain of bicarbonate, raising the blood’s pH. Vomiting fits this perfectly because it expels gastric acid (hydrochloric acid), removing H+ from the body and also often causing chloride depletion. That loss of acid and chloride shifts the body toward a more bicarbonate-dominant state. Additionally, the resulting volume depletion from vomiting activates mechanisms that promote bicarbonate reabsorption in the kidneys and further hydrogen ion loss, which sustains the alkalosis. The respiratory system can compensate by hypoventilating to raise CO2, but this compensation is limited and cannot fully correct the elevated bicarbonate.

Other options don’t align with metabolic alkalosis: salicylate poisoning can cause respiratory alkalosis early and metabolic acidosis later; uncontrolled diabetes mellitus leads to metabolic acidosis (diabetic ketoacidosis); renal failure typically causes metabolic acidosis due to acid buildup.