Interconversion and comparison of the results of three methods for cholinesterase in serum.

We investigated three methods for determination of cholinesterase (ChE) in human blood sera, using reference sera, sera of known ChE content, and serum variously diluted with deactivated sera. The methods were the Du Pont aca analyzer, the Pfizer "ChE-tel" method, and the Michel method with and without direct reagent-blank correction. With respect to precision and reproducibility the methods ranked: aca greater than Michel method corrected directly for reagent pH changes (Michel) greater than ChE-tel method greater than Michel method corrected indirectly for reagent pH changes. The interrelationships derived, in terms of each method's individual units were: Michel = (0.054 +/- 0.001) aca - (0.043 +/- 0.086), r2 = 0.947 ChE-tel = (4.44 +/- 0.30) aca - (5.11 +/- 0.99), r2 = 0.959 ChE-tel = (80.2 +/- 5.8) Michel + (0.028 +/- 0.240), r2 = 0.947 The ChE-tel method was subject to variations due to the quality of different kits. The aca results were validated by a collaborative laboratory study. Sera of known activity can be used effectively for accurate calibration.