A 28-year-old farmer is brought unconscious with miosis, bradycardia, excessive secretions and fasciculations after spraying insecticide. Which specific biochemical test on blood BEST confirms organophosphorus poisoning and helps distinguish it from carbamate poisoning?

• A Plasma pseudocholinesterase (butyrylcholinesterase) activity alone
• B Urinary alkyl phosphate metabolite measurement
• C Whole-blood acetylcholinesterase (RBC-ChE) activity with spontaneous reactivation test over 24 hours ✓
• D Serum atropine level

Explanation

RBC cholinesterase (true acetylcholinesterase) is more specific to cholinergic nerve function. The spontaneous reactivation test distinguishes OP (where inhibition is largely irreversible within hours due to 'ageing') from carbamate poisoning (where the carbamylated enzyme spontaneously reactivates within hours because carbamylation is reversible). Plasma pseudocholinesterase is more sensitive but less specific. Urinary alkyl phosphates confirm OP exposure but are not routinely used for acute clinical distinction; serum atropine is a therapeutic agent, not a diagnostic marker.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.