Simultaneous automated measurement of serum total CK and CK-MM isoform ratio in serum

We automated a two-step kinetic procedure for determining serum CK-MM isoform ratio using an immunoinhibition method. By measuring the total CK activity and the residual CK activity (serum CK-MM isoform) remaining after the inhibition by tissue CK-MM isoform specific monoclonal antibody reagent (CK-M01) the CKMM isoform ratio is calculated using the difference between total CK and residual CK activities divided by the residual CK activity. Linearities of total CK and residual CK assays were < or = 7750 U/L and 2,500 U/L, respectively; within-run CVs of isoform ratio (N = 10) were 2.8 and 7.0% (mean 0.14 and 0.60), respectively. The MM3/MM1 isoform ratio obtained with the proposed method (X) correlated well with the results of electrophoretic method (Y) according to the equation: Y = 0.98X-0.3, r = 0.988. The normal reference range of isoform ratios obtained by assaying 1,222 serum samples from healthy subjects was 0.09-0.75. The isoform ratio increased after onset of chest pain, peaking at 2-6 hr thereafter. A mean isoform ratio of 1.86 was obtained with serum sample from 86 patients diagnosed as having an acute myocardial infarction (AMI). This method is accurate and highly sensitive, as the detection and early diagnosis of AMI can be completed in 10 min.