Screening for plasma cholinesterase deficiency: an automated succinylcholine based assay.

We describe an automated kinetic method that uses a single aqueous reagent to measure the in vitro hydrolysis of the muscle relaxant succinylcholine. The substrate succinylcholine is hydrolyzed by plasma cholinesterase (EC 3.1.1.8), and the choline produced is oxidized by choline oxidase (EC 11.3.17) in the presence of peroxidase, 4-aminophenazone and phenol, to yield a chromagen with maximum absorbance at 500 nm. The method is reproducible (CV 1.3%), correlates well with a manual procedure using the same substrate (r = 0.994, y = 0.99x - 0.25), and is linear to 150 U/L. The method is well suited to pre-operative screening and detection of "at-risk" individuals, as illustrated by the family of one patient who had a prolonged succinylcholine apnea.