A healthy young man scheduled for day-care surgery under general anaesthesia gives a history of prolonged apnoea requiring ventilation in his brother after a minor procedure. Preoperative testing shows plasma cholinesterase activity is normal. The next most appropriate test to identify the inherited defect responsible is measurement of:

• A Dibucaine number ✓
• B Fluoride number only
• C Serum butyrylcholinesterase genotype by karyotyping
• D Acetylcholine receptor antibody titre

Explanation

The dibucaine number measures percentage inhibition of plasma cholinesterase by dibucaine. The usual homozygous normal individual shows about 80 percent inhibition, heterozygotes about 60 percent, and persons with the atypical dibucaine-resistant variant show below 30 percent despite normal total enzyme activity. Since baseline cholinesterase activity is normal in this family, activity alone misses the defect, and the dibucaine number identifies the qualitative atypical enzyme that causes suxamethonium apnoea.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.