Immunochemical determination of CK-MB isoenzyme in human serum: a radiometric approach

The presence of creatine kinase isoenzyme MB (CK-MB) in human serum is an indicator of myocardial injury. In this assay for CK-MB, reagent containing both rabbit antibodies to CK-MM and 125I-labeled sheep antibodies to CK-BB is added to the patient's serum and incubated for 1 h at ambient temperature. Goat anti-rabbit immunoglobulin, conjugated to a mixture of amylose and polyvinylidene fluoride floccules, is then added. After a 15-min incubation, the mixture is centrifuged, isolating the two M-subunit-containing isoenzymes as insoluble complexes. Because the B-subunit portion of MB is labeled with 125I, the radio-activity in the pellet will be proportional to the amount of MB present. The discarded supernate contains excess sheep 125I-labeled BB antibodies, free or bound to BB isoenzyme if it is present. The preparation and characterization of the isoenzymes and antibodies is explained. Concentrations of CK-MB is sera of patients with and without an acute myocardial infarction were assayed in serial specimens obtained in 103 consecutive admissions to a coronary care unit. The performance of this radiometric procedure compared well with CK-MB electrophoresis, giving a sensitivity of 100% and a specificity of 92%.