Critical difference between serial measurements of CK-MB mass to detect myocardial damage

To assess the critical difference in serial measurements of CK-MB(mass) and the ability of this critical difference to detect myocardial damage, we studied 110 patients in whom an acute myocardial infarction (AMI) had been ruled out. Blood samples were drawn at 3, 4, 5, 6, 7, 8, 12, 16, 20, and 24 h after onset of symptoms. With a critical difference of 72.6%, an increase of > 2.0 mu g/L between two CK-MB(mass) measurements was determined to be significant. Twenty-three of the non-AMI patients had an increase in CK-MB(mass) > 2.0 mu g/L, but five of these did not have an abnormal concentration of troponin T (i.e., not > 0.1 mu g/L). Also among the 110 non-AMI patients, 22 did have an abnormal troponin T value, 18 of whom (82%) also had CK-MB(mass) increased by > 2.0 mu g/L. In 20 of the 23 patients with an increase in CK-MB(mass) > 2.0 mu g/L, this increase was detected from the values for two samples collected at 5 and 12 h after onset of symptoms. In conclusion, using the critical difference for CK-MB(mass) defined as an increase > 2.0 mu g/L detected myocardial damage in patients without AMI.