Distal renal tubular acidosis (Type 1 RTA) is characterised by all of the following EXCEPT:

• A Urine pH >5.5 despite systemic acidosis
• B Elevated serum ammonia with reduced urinary ammonium ✓
• C Hypokalaemia
• D Hyperchloraemic normal anion gap metabolic acidosis

Explanation

Type 1 RTA results from failure of alpha-intercalated cells to secrete H+ in the collecting duct; features include urine pH persistently >5.5 (inability to acidify urine), hypokalaemia (K+ wasted as Na+ is reabsorbed via non-H-ATPase channels), and hyperchloraemic normal AG metabolic acidosis. Serum ammonia is NOT elevated — ammonia excretion as ammonium is reduced because the collecting duct cannot lower urinary pH to trap NH4+, but hepatic ammonia is normal. Elevated serum ammonia is a feature of urea cycle disorders.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.