Creatine kinase B subunit as measured with a radioimmunoassay kit in detection of acute myocardial infarction.

Results with a commercial radioimmunoassay (RIA) reagent kit for quantification of the creatine kinase B subunit (CK-B) (Nuclear-Medical Laboratories, Irving, TX 75061) were compared with results obtained by electrophoresis for patients consecutively admitted to our coronary care unit for suspected acute myocardial infarction. Analytical sensitivity, precision, and specificity of the RIA were satisfactory. Its clinical efficacy was assessed in 97 patients suspected of having had an acute myocardial infarction. Of 30 patients who had had an acute myocardial infarction, increased CK-B was detected by RIA in 30 and by electrophoresis in 27. The temporal relationship between CK-B by RIA and CK-MB by electrophoresis was similar. Of 66 admissions where infarction was not established, CK-B was negligibly increased in samples from four patients by RIA, and from one by electrophoresis. Although not abnormally increased (greater than 5 U/L), CK-MB was detected by electrophoresis in samples from another five of these 66 patients. We conclude that estimation of CK-B by this RIA is an excellent alternative to estimation of CK-MB by electrophoresis in patients suspected of having had an acute myocardial infarction.