In the present study, the cause of suspected false-positive (anomalous) values for CK-MB activity, in Indian patients investigated for ACS. Total serum CK and CK-MB activity, serum Troponin I were measured and CK-MB as a percentage of the total CK activity (%CK-MB) calculated. CK-MB was also estimated using densitometry and CK-MB mass assay. Anomalous specimens were tested for the presence of CK isoenzymes. In 22 healthy subjects, 11 male and female, the %CK-MB ranged from 3.6 to 30.2. In 11 male patients, with proven ACS, the %CK-MB was from 4.0 to 17.5. The cut off for anomalous CK-MB activity values was set as >33.0%. In 35 patients with anomalies, total CK values ranged from 39 to 231 U/L, CK-MB from 30 to 161 U/L. Investigation of CK isoenzymes, showed 10 patients had a CK-BB band, 14 an intermediate band between CK-MM and CK-MB (macro-CK type 1), 7 had a cathodal band (macro-CK type 2), and 3 had a band intermediate between CK-MB and CK-BB. This later band does not seem to have been previously reported. Against the CK-MB mass assay, the activity assay showed no correlation, in 43 patients (19 M, 24 F), Pearson coefficient (R(2)) was 0.006. The CK-MB immunoinhibition assay is better described as measuring "non-CK-MM activity." A %CK-MB activity >6% as a marker of ACS is not valid in our patient population. Laboratories should not use only CK-MB activity as a biochemical marker of ACS.
Keywords: Acute coronary syndrome; Anomalies; Biochemical markers; CK-MB isoenzymes; Macro-creatine kinase.