Interference of CK-BB isoenzyme in the determination of CK-MB using the immunoinhibition method in patients with pulmonary diseases

An increase in serum creatine kinase-MB (CK-MB) isoenzyme is regarded as a specific indicator of acute myocardial infarction. We analyzed retrospectively the clinical data of 94 patients whose serum creatine kinase MB (CK-MB) was measured with immunoinhibition kit which measures all residual CK activity following inactivation of M-subunit. There were 21 patients with chronic obstructive lung disease (COLD), 17 patients with pneumonia, 17 patients with pulmonary tuberculosis (TBC), 16 patients with non-small cell lung cancer (NSCLC), 10 patients with small cell lung cancer (SCLC), 8 patients with malignancies of other origin (NPL), and 5 patients with chronic heart diseases. The results revealed that serum concentrations of CK-MB in SCLC, NSCLC and TBC were significantly greater than those in other groups (P < 0.1). Clinical examination showed no evidence of myocardial infarction, injury, or tumor involvement of the heart. We assumed that those results are due to interference of the CK-BB isoenzyme in the immunoinhibition method. So we suggest that in clinical practice, markedly elevated levels of CK-MB measured with immunoinhibition kit, after the exclusion of the myocardial injury, may point toward the existence of a malignancy or TBC of the lungs.