A 24-year-old woman ingests an unknown clear liquid in a suicide attempt. She complains of severe burning in the mouth and throat, and within hours develops carpopedal spasm with a positive Chvostek sign. Urine examination shows abundant colorless, envelope-shaped crystals. Which substance did she ingest?
- A Sulphuric acid
- B Carbolic acid
- C Oxalic acid ✓
- D Nitric acid
Correct answer: C. Oxalic acid
Explanation
Oxalic acid is both locally corrosive and systemically toxic because it binds ionized calcium to form insoluble calcium oxalate, producing hypocalcaemic tetany and envelope-shaped calcium oxalate crystals in urine. The tetany plus crystalluria clinches it. Cystine crystals are hexagonal plates and occur in cystinuria without hypocalcaemia, so they would not explain the Chvostek sign. Sulphuric and nitric acids are purely corrosive and do not chelate calcium.
Reference: Essentials of Forensic Medicine and Toxicology, R.K. Narayan Reddy, 33rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.