Evaluation of a new method for cholinesterase determination.

We report the evaluation of a new commercially available assay system for determination of the catalytic activity of serum cholinesterase (EC 3.1.1.8) and application of the method to a centrifugal fast analyzer. Serum cholinesterase activity is determined at 30 degrees C using para-hydroxybenzoylcholine as substrate. This reaction is coupled to a second reaction using para-hydroxybenzoate hydroxylase (EC 1.14.13.2) as coupling enzyme. Enzyme activity is measured kinetically by monitoring the decrease in absorbance at 340 nm of NADPH in the second reaction. The procedure is precise and the results obtained from normal and pathological sera show good correlation with those obtained by the alternative procedures employing propionylthiocholine, butyrylthiocholine and benzoylcholine as substrates. The reference range for 700 healthy subjects was estimated to be 140-345 U/L (95% central range, determined non-parametrically), with significant difference between males and females (155-353 U/L for men and 134-323 U/L for women, p less than 0.001).