Reliability and Significance of Increased Creatine Kinase MB Isoenzyme in the Serum of Uremic Patients

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Abstract
The authors quantified creatine kinase MB (CK-MB) isoenzyme activity and mass in the serum of 81 uremic and 20 nonuremic (control) patients who had no clinical or electrocardiographic evidence of acute myocardial infarction. CK-MB was quantified by three methods: electrophoresis, the QuiCK-MB® (International Immunoassay Labs), and the Tandem-E® CK-MB (Hybritech, Inc.). The authors then followed all uremic patients for subsequent hospitalization for cardiac disease. Median CK-MB was increased in the serum of the uremic patients as compared with the control patients by all methods. Most uremic patients had CK-MB in serum above the median CK-MB of the control group. Seventeen (21%) uremic patients had CK-MB in serum elevated above the reference range by at least one method. All control patients had CK-MB in the serum within the reference range. Twelve of 81 (15%) uremic patients have subsequently developed acute myocardial infarction (six patients; four died) or angina pectoris (six patients; one died). Eleven patients were specifically hospitalized for cardiac symptoms. One patient had acute myocardial infarction three weeks after renal transplant. With the use of the chi-square test and 2×2 contingency tables, patients with CK-MB in serum above 5 U/L by electrophoresis (χ2 = 5.47; P < 0.05) or at least 2.9 EU/L by the QuiCK-MB (χ2 = 6.56; P < 0.01) appeared to be at increased risk of subsequent hospitalization. The authors conclude that a slight increase of CK-MB in serum is found in most uremic patients. However, CK-MB elevated above reference range in the serum of uremic patients without clinical or electrocardiographic evidence of acute myocardial infarction is not common. When found, elevated CK-MB isoenzyme appears to be associated with an increased risk of subsequent cardiac disease. Therefore, quantification of CK-MB in the serum of uremic patients is more reliable than is implied in the literature.