A two-site immunoradiometric assay for the MB isoenzyme of creatine kinase.

A two-site immunoradiometric assay for myocardial creatine kinase MB isoenzyme is described. The method utilizes immobilized anti-human creatine kinase BB antibodies and 125I-labelled anti-human creatine kinase MM antibodies and can specifically detect creatine kinase MB in the presence of approximately 1000-fold excess of creatine kinase MM or BB. Native creatine kinase MB prepared from human heart and creatine kinase MB prepared by hybridisation of purified human creatine kinase MM and creatine kinase BB appeared to react identically in the assay. Serum estimations on patients with suspected myocardial infarction correlated with the presence of an MB band on electrophoresis but preliminary results suggest that the two-site immunoradiometric assay may be more sensitive.