Plasma cholinesterase genetic variants phenotyped using a Cobas-Fara centrifugal analyser

A two-step colorimetric method that overcomes the difficulties of the classic 240 nm benzoylcholine assay for plasma cholinesterase has been adapted to a Cobas-Fara centrifugal analyser, using choline oxidase coupled with peroxidase/phenol/aminoantipyrine for detection of the choline produced. Reaction conditions of the main reaction are identical to those of the classical benzoylcholine assay. The described method was applied to 105 selected serum samples, previously classified by the Danish Cholinesterase Research Unit as homo- or heterozygous for the usual (U), atypical (A), fluoride-resistant (F), or silent (S) allelic variants. The method showed a distinct separation of the various phenotypes, with catalytic activity concentrations, dibucaine numbers, and fluoride numbers directly comparable to established reference values of the manual 240 nm benzoylcholine method.