A young adult develops prolonged apnea after receiving succinylcholine during anesthesia. Family history reveals a sibling had a similar reaction. Which laboratory finding BEST explains this susceptibility?
- A Elevated serum acetylcholinesterase activity
- B Low dibucaine number reflecting abnormal pseudocholinesterase ✓
- C Reduced serum cholinesterase due to chronic liver disease alone
- D Presence of macro-CK type 2 in serum
Correct answer: B. Low dibucaine number reflecting abnormal pseudocholinesterase
Explanation
Succinylcholine is hydrolyzed by plasma pseudocholinesterase (butyrylcholinesterase). In hereditary deficiency, an atypical enzyme with reduced affinity for substrate persists, detected by the dibucaine number: normal enzyme is inhibited about 80 percent by dibucaine, while the atypical homozygote shows inhibition near 20 percent, giving a low dibucaine number. Acquired deficiency from liver disease or organophosphates causes milder, transient prolongation.
Reference: Harper's Illustrated Biochemistry, 31st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.