AN IMMUNOINHIBITION ASSAY FOR DETERMINATION OF CREATINE-KINASE ISOFORMS IN SERUM

We report a preliminary evaluation of an immunoinhibition assay for cr eatine kinase isoform quantification. The procedure employs the monocl onal antibody CKM-G01, which inhibits the native M subunit of creatine kinase. The antibody does not inhibit the M subunit modified by remov al of lysine by plasma carboxypeptidase N. Residual activity after tre atment with the antibody is therefore due to serum delysinated isoform s. The ratio inhibited/residual activity correlated directly with the ratio tissue/serum isoforms. Analysis of the total imprecision of isof orm ratio measurement gave a coefficient of variation between 5.9 and 21.1%. Reference intervals for the ratio were 0.14-0.79 in females and 0.19-0.95 in men (p = 0.0046). Analytical and clinical comparison wit h alternative isoform procedures gave good results, showing that this assay can be used as alternative to the widely accepted electrophoreti c method for measurement of the creatine kinase isoform ratio.