Discordant results of CK-MB and troponin I measurements: a review of 14 cases

In the course of a clinical comparison involving 204 parallel total creatin e kinase (CK), creatine kinase-MB isoenzyme (CK-MB), and cardiac troponin I (cTnI) measurements, 12 patients were identified in whom cTnI was elevated while total CK was normal, as well as 2 patients in whom CK-MB was elevate d while cTnI was normal. CK-MB relative index was elevated in 6 of the twel ve cTnI-positive patients with normal total CK; only 2 of these patients ha d a discharge diagnosis of acute myocardial infarction (AMI). All of the 12 patients in this group had medical conditions that are associated with gre ater risk for acute cardiac events. Both patients with normal cTnI but elev ated total CK and CK-MB index had chronic renal insufficiency; one of these patients had a positive stress test and a diagnosis of AMI. The other cTnI -negative patient died 2 days after admission, and autopsy revealed evidenc e of ischemic changes, but not acute infarction. Significant differences we re apparent between traditional CK-MB results and cTnI measurements. Using total CK elevation as a prerequisite for subsequent CK-MB measurement may l imit the clinical sensitivity of this enzyme marker for detecting subacute ischemic damage to the myocardium. Elevated total CK and CK-MB isoenzyme wi thout corresponding elevations in cTnI, on the other hand, may reflect chan ges in enzyme elimination kinetics due to renal failure, or cross-reactivit y of the cTnI assay with non-cardiac antigens.