A pyloric stenosis is most consistently associated with which electrolyte pattern?

• A. Hyperchloremic metabolic acidosis with hypokalemia.
• B. Hyperkalemia with metabolic acidosis.
• C. Hypochloremic metabolic acidosis with hypokalemia.
• D. Hypochloremic metabolic alkalosis with hypokalemia.

Answer: (D)

Vomiting gastric contents in pyloric stenosis causes loss of hydrogen and chloride from the stomach, and significant fluid depletion. Losing hydrogen ions and chloride raises the body’s bicarbonate level, producing metabolic alkalosis, while the chloride loss keeps the pattern hypochloremic. The dehydration activates the renin–angiotensin system, leading to increased potassium loss in the kidneys, so potassium becomes low. The combination of low chloride, metabolic alkalosis, and hypokalemia fits the classic pattern seen with pyloric stenosis, due to the gastric fluid losses and compensatory renal responses.