In 195 patients presenting with chest pain and referred acutely for cardiological assessment, blood was taken immediately for assay of creatine kinase (CK; EC 2.7.3.2) MB isoenzyme by an immunochemical method and results [mass units of enzyme per liter of plasma (microgram/L)] were obtained within 30 min of sampling. Diagnosis of acute myocardial infarction in the patients was made independently, based on electrocardiograms and conventional cardiac enzyme profiles. The administration of any thrombolytic therapy in response to the CK-MB concentration result was also noted, allowing assessment of the assay's potential influence on patient management in addition to the diagnostic efficiency evaluation. The study demonstrated that, when blood samples were collected on admission to hospital and the decision level suggested by the manufacturers was utilized, the assay had an immediate sensitivity of 52% and a specificity of 97%. Of the 81 patients who were shown by conventional means to have had acute myocardial infarction, 8 (10%) had equivocal electrocardiograms but positive CK-MB concentration results. In four of these patients (5%), thrombolytic therapy was given on the basis of the clinical features and a positive CK-MB concentration result alone.
