Which acid-base disorder commonly accompanies CKD and what causes it?

• A. Metabolic alkalosis due to vomiting
• B. Metabolic acidosis due to decreased bicarbonate reabsorption and acid excretion
• C. Respiratory acidosis due to hypoventilation
• D. Metabolic acidosis due to increased bicarbonate reabsorption

Answer: (B)

Chronic kidney disease commonly causes metabolic acidosis because the kidneys lose the ability to excrete daily acid loads and to reclaim and regenerate bicarbonate. As nephrons fail, ammoniagenesis and acid excretion decline, so acid builds up in the body. At the same time, bicarbonate reabsorption and generation decrease, leading to bicarbonate loss in the urine and a fall in serum bicarbonate. The net effect is a metabolic acidosis, typically a non-anion gap (hyperchloremic) type, with the body trying to compensate by increasing ventilatory effort to blow off CO2. This is why the best answer describes metabolic acidosis due to decreased bicarbonate reabsorption and acid excretion. The other options describe conditions that aren’t characteristic of CKD—alkalosis from vomiting, respiratory acidosis from hypoventilation, or acidosis from increased bicarbonate reabsorption would not fit the typical CKD pattern.