The objective of this study was to apply Passing-Bablok regression and estimate the systematic error (SE) at two levels of enzyme activity. The External Quality Assessment Program (EQAP) and BioRad Unity Next Peer QC were used. For alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyltransferase (GGT), creatine kinase (CK), and amylase (AMI), the ES for level 1 were: 0.4; 1.8; 1.6; 2.6; -2.4; -0.3, and for level 2: 3.3; 14; 13.4; 18.5; -8.3; 10.7, based on the regression equations (r≥0.93; p<0.0001). The 95% CIs for the intercept and slope were analysed, and it was concluded that the SE component was constant and proportional for CK and AMI. However, it was proportional for the other enzymes. This method could be the preferred method because it allows estimating and determining the SE composition.
