Unmasking artifactual increases in creatine kinase isoenzymes in patients with renal failure

Previous reports have suggested that creatine kinase isoenzymes are elevated in patients with chronic renal failure and thus are less useful in the evaluation of chest pain in such patients. Our data in 88 patients with chronic renal failure receiving maintenance dialysis confirm this observation for total plasma creatine kinase. However, elevations in MB and BB creatine kinase, although statistically significant, were biologically unimpressive (5.9 ± 0.05 [SEM] IU/L compared with 4.8 ± 0.04 IU/L for MB creatine kinase [p < 0.02], and 5.5 ± 0.08 ng/ml compared with 3.2 ± 0.05 ng/ml for BB creatine kinase [p < 0.0002]), and were unlikely to cause diagnostic confusion. In 92% of patients with chronic renal failure, plasma MB creatine kinase activity was within the normal range (<13 IU/L). Eight percent of patients manifested abnormal MB creatine kinase values; the highest was 20 IU/L. The glass bead method for measuring MB creatine kinase was used to avoid the potential confusion induced by non-creatine kinase-mediated fluorescence, which occurs in the region of MB and BB creatine kinase on electrophoresis. The infrequent and modest increases in plasma MB creatine kinase observed in patients with chronic renal failure should be appreciated, but it should not cause diagnostic confusion, because acute myocardial infarction usually results in more substantial elevations of MB creatine kinase.