Development and clinical evaluation of a microcentrifugal analyzer method for determining creatine kinase MB isoenzyme.

We have adapted to a microcentrifugal analyzer an immunoinhibition assay for measuring the activity of creatine kinase MB by using an inhibitory antibody for the M monomer. The method actually measures half the MB activity, but results are not multiplied by two because atypical isoenzymes of creatine kinase, including BB, IgG-BB, and the isoenzyme derived from mitochondria, are also detected, if they are present. Results correlated well with an electrophoresis method for 36 serum samples. Myocardial infarction was assessed in 175 patients admitted to our coronary-care unit, with respect to sensitivity (100%) and specificity (98%) when a decision point of 100 U/L (30 degrees C) was chosen for total creatine kinase activity (dithiothreitol-activated) and 6 U/L (30 degrees C) for the isoenzyme (by immunoinhibition). Atypical isoenzymes are easily recognized and confirmed by electrophoresis when the MB activity (by immunoinhibition) exceeds 6 U/L and 20% of the total creatine kinase activity.