A patient with chronic kidney disease stage G4 (eGFR 22 mL/min) has serum bicarbonate of 16 mEq/L, pH 7.28, and anion gap of 18 mEq/L. The MOST likely acid-base disorder is:
- A High anion gap metabolic acidosis due to uraemic organic acid accumulation ✓
- B Non-anion gap metabolic acidosis (renal tubular acidosis)
- C Type 4 RTA (hyperkalaemic, hyperchloraemic) secondary to hyporeninaemic hypoaldosteronism
- D Respiratory alkalosis with metabolic compensation
Correct answer: A. High anion gap metabolic acidosis due to uraemic organic acid accumulation
Explanation
Late-stage CKD (stages 4–5) causes high anion gap metabolic acidosis due to impaired renal excretion of phosphates, sulphates, hippurate, and other organic acids produced by protein metabolism (uraemic acidosis). The anion gap of 18 and low bicarbonate confirm HAGMA. Early CKD (stages 1–3) more commonly causes non-anion gap (hyperchloraemic) metabolic acidosis due to impaired NH₄⁺ excretion. Type 4 RTA occurs typically in early CKD with diabetic nephropathy.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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