A 5-year-old child presents with failure to thrive, polyuria, polydipsia, and recurrent episodes of dehydration. Blood investigations show pH 7.30, HCO3 16 mEq/L, serum potassium 2.8 mEq/L, serum chloride 112 mEq/L, and anion gap 12 mEq/L (normal). Urine pH is 6.8 despite acidosis. What is the most likely diagnosis?

• A Proximal renal tubular acidosis (Type 2)
• B Distal renal tubular acidosis (Type 1) ✓
• C Type 4 renal tubular acidosis
• D Diabetic ketoacidosis

Explanation

This is distal (Type 1) RTA: normal anion gap metabolic acidosis with hypokalemia, inability to acidify urine (urine pH >5.5 despite systemic acidosis), and complications like failure to thrive and nephrocalcinosis. In proximal RTA (Type 2), urine can be acidified (pH <5.5) when serum HCO3 is low. Type 4 RTA has hyperkalemia. DKA has an elevated anion gap and ketonuria.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.