Optimal diagnosis of myocardial infarction using only cardiac specific isoenzymes

Abstract

The routine serial measurement of creatine kinase cardiac specific isoenzyme (CKMB) by a modified immunoinhibition method adapted to common discrete analysers (ABBOTT ABA 100 and Centrifichem 400) has been shown to be diagnostically accurate by a clinical trial involving 151 consecutive admissions to a coronary care unit. To minimize the possibility of missing a myocardial infarction (MI) due to the rapid clearance of CKMB (36-48 h), heat stable lactate dehydrogenase (a cardiac specific isoenzyme having slow clearance) was measured if indicated. The predictive value (PV) of the measured enzymes was derived using the discharge diagnosis. PV positive gives the likelihood for the presence of the disease in a patient with a positive result. PV negative estimates the likelihood for freedom of disease in a patient with a negative result. Effectiveness is a measure of the overall diagnostic accuracy of a particular test. Predictive value of CKMB CK AST CK & AST PV positive 0.90 0.91 0.76 0.91 PV negative 1.00 1.00 1.00 1.00 Effectiveness 0.99 0.96 0.87 0.87 Routine measurement of isoenzymes on discrete analysers leads to earlier and more accurate diagnosis of MI without increased laboratory costs.