Modification of an automated method for determining plasma and erythrocyte cholinesterase activity in laboratory...

By altering the analytical parameters on an automated analyzer, analytical precision for measuring cholinesterase (ChE) activity in hemolysates was markedly improved in samples from several species. Manual and automated spectrophotometric analyses of plasma and erythrocyte ChE activity were optimized for use in rats, mice and dogs. Replicate ChE analyses were performed on plasma samples and on hemolysates made from whole blood or packed erythrocytes to determine the precision of the manual ChE method and 4 modifications of the automated method. Large method-related differences in precision were observed for the erythrocyte assay, but not the plasma assay. The addition of a nonionic detergent to make hemolysates was beneficial in determining erythrocyte ChE activity in the rat, but not in the mouse or dog. Species specific temperature conversion factors were necessary for comparing results from methods using different analytical temperatures. Analysis of whole blood hemolysates provided similar or better precision for determining erythrocyte ChE activity compared to using hemolysates made from packed erythrocytes. Comparisons of erythrocyte ChE results obtained from assays with even minor methodological differences should be approached with caution because of the many analytical factors which can affect results.