FACTORS IN STANDARDIZING AUTOMATED CHOLINESTERASE ASSAYS

A scientific panel assembled by the U.S. Environmental Protection Agen cy (EPA) determined that variability in cholinesterase (ChE) activitie s in the agency's pesticide/animal study database likely was due to a lack of accepted guidelines for ChE methodology. A series of trials wa s held in which participating laboratories measured ChE activity in bl ood and brain samples from untreated and pesticide-treated rats using a colorimetric assay method. The degree of inhibition of ChE activity in plasma and brain samples compared to controls was consistent among most of the laboratories. The ChE activity in erythrocyte samples diff ered more between laboratories due to a high blank, low erythrocyte AC hE activity and hemoglobin absorption at the wavelength of the assay. Strategies are suggested for minimizing the variability of ChE activit y in hemoglobin-rich samples.