A 28-year-old farmer is brought to the emergency department with profuse salivation, miosis, bradycardia, and muscle fasciculations. His serum butyrylcholinesterase activity is markedly depressed. Which enzyme assay is considered the MOST sensitive and specific indicator of organophosphate toxicity at the tissue level?
- A Red blood cell (erythrocyte) acetylcholinesterase ✓
- B Butyrylcholinesterase (plasma cholinesterase)
- C Serum alanine aminotransferase
- D Urinary delta-aminolevulinic acid
Correct answer: A. Red blood cell (erythrocyte) acetylcholinesterase
Explanation
RBC acetylcholinesterase (true cholinesterase) reflects synaptic enzyme inhibition more accurately than plasma butyrylcholinesterase because it is structurally identical to the nerve terminal enzyme. Plasma butyrylcholinesterase is more sensitive (falls earlier) but is less specific, being reduced by liver disease and genetic variants. RBC AChE depression above 25% correlates with clinical toxicity and is used to monitor recovery after pralidoxime therapy. Urinary delta-ALA is a biomarker for lead poisoning, not OP toxicity.
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.