Incremental value of the leukocyte differential and the rapid creatine kinase-MB isoenzyme for the early diagnosis of myocardial infarction

Objective: To test whether automated measurements of cortisol-induced changes in the leukocyte differential can provide an early marker of myocardial infarction, especially when combined with the rapid creatine kinase-MB isoenzyme. Design: A prospective, blinded study of these measurements at the time of initial assessment in the emergency department. Setting: Large multispecialty clinic hospital. Patients: 511 consecutive patients presenting to the emergency department with chest pain. One hundred twenty-seven patients with infection, trauma, or metastatic cancer or receiving myelosuppressive or glucocorticoid therapy were excluded. Measurements: Automated leukocyte differentials, rapid creatine kinase-MB levels, cortisol levels, and routine clinical measurements. Results: Of 69 patients with myocardial infarction, only 39% had diagnostic electrocardiographic ST-segment elevation. ST-segment elevation had a specificity of 99% and a positive predictive value of 93%. A relative lymphocytopenia (lymphocyte decrease <20.3%) or elevated rapid creatine kinase-MB level (>4.7 ng/mL) was more sensitive than ST-segment elevation (sensitivities of 58% and 56%, respectively) but less specific (specificities of 91% and 93%, respectively). The presence of both a relative lymphocytopenia and an elevated rapid creatine kinase-MB level had a sensitivity of 44%, a specificity of 99.7%, and a positive predictive value of 97% (95% CI, 80% to 99%). Both a relative lymphocytopenia and an elevated rapid creatine kinase-MB level were independent (P < 0.001) predictors of infarction in patients without ST-segment elevation. If myocardial infarction was suspected by the presence of both abnormal markers or ST-segment elevation, the sensitivity for early diagnosis increased from 39% (ST elevation alone) to 65% (CI, 52% to 76%); the specificity was 99%; and the positive predictive value was 94% (CI, 82% to 98%). Conclusions: The presence of both a relative lymphocytopenia and an elevated rapid creatine kinase-MB level was an accurate early marker of myocardial infarction that appeared to improve the sensitivity of early diagnosis compared with that of ST-segment elevation alone.