The anion gap (AG) in a patient with normal albumin is calculated as Na+ − (Cl− + HCO3−). Which condition causes an elevated AG metabolic acidosis without an elevated lactate or ketones?

• A Diarrhoea (loss of HCO3−)
• B Type 1 renal tubular acidosis
• C Hyperchloraemic acidosis from normal saline infusion
• D Ethylene glycol poisoning (oxalate accumulation) ✓

Explanation

Ethylene glycol is metabolized to oxalic acid and glycolic acid, which are unmeasured anions causing elevated AG metabolic acidosis (HAGMA). Diarrhoea causes HCO3− loss — a normal AG (hyperchloraemic) acidosis. Type 1 RTA also causes normal AG acidosis due to impaired H+ excretion with compensatory Cl− retention. Large-volume normal saline infusion dilutes HCO3− and raises chloride, producing hyperchloraemic (normal AG) acidosis.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.