Comparison of seven serum assays on four automatic analysers

Serum enzyme assays used on four different analysers (Hitachi 737, Hitachi 705, Cobas-bio and RA-2X) were compared by determining the activity of seven different enzymes (AST, ALT, LD, ALP, GGT, CK and AMS). Performance checks (quality control procedure) and replications (the study of the total analytic imprecision and of its components) were conducted and the methods were compared by linear regression analysis with statistical inference on the curves following the protocols of the National Committee for Clinical Laboratory Standards (NCCLS: PSEP- 2, PSEP-3, PSEP-4). The correlation coefficients between the methods (r = 0.991-0.999), together with the other statistical parameters, indicated that the methods are well correlated on all the instruments. The total imprecision was good for all analytes, except ALT. Among the instruments tested, the RA-2X gave more variable results, although the total imprecision was acceptable. There was no relevant carry-over effect. The evaluation of performance claims indicated that the expected error did not substantially affect the results at the level of clinical decisions.