A 30-year-old man presents with high anion gap metabolic acidosis and hypocalcemia after ingesting antifreeze. Urine microscopy shows characteristic envelope-shaped crystals. Which metabolite binds with serum calcium to form these crystals?
- A Oxalic acid ✓
- B Glyoxylic acid
- C Glycolic acid
- D Formic acid
Correct answer: A. Oxalic acid
Explanation
Ethylene glycol is metabolized by alcohol dehydrogenase into glycolic acid, glyoxylic acid, and finally oxalic acid. Oxalic acid binds with serum calcium to form calcium oxalate crystals, which deposit in the kidneys and vasculature. Glycolic acid primarily drives the high anion gap metabolic acidosis seen in these patients. Formic acid is the toxic metabolite responsible for the toxicity in methanol poisoning.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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