[Muscle enzymes in differential diagnosis of acute myocardial infarction and rhabdomyolysis. Evaluation of the parameter creatine kinase isoenzyme MB index (CKMB index)].

Both serum creatine kinase activity (CK) and creatine kinase isoenzyme MB mass concentration (CKMB) may be elevated in patients with either skeletal muscle damage or myocardial infarction. In a prospective study we evaluated the parameter CKMB index in discriminating these different events in 70 hospitalised patients with elevated CK-values, of whom 38 satisfied the WHO criteria for acute myocardial infarction. The sensitivity and specificity of the index for diagnosing myocardial infarction with various cut-off values between negative and positive tests are presented. A maximal CKMB index in a series of blood samples exceeding 5.0 is diagnostic of myocardial infarction, while a maximal value lower than 3.0 virtually excludes this diagnosis. An index of more than 3.0 in a single test makes rhabdomyolysis improbable and is strongly indicative of acute myocardial infarction. We conclude that CKMB index may be a valuable diagnostic tool in the differential diagnosis of myocardial infarction versus muscle damage.