Immunochemical extraction and automated measurement of plasma creatine kinase MB isoenzyme and creatine kinase MB 2 isoform

Measurement of creatine kinase MB (CK‐MB) and its isoforms CK‐MB 2 and CK‐MB 1 are now applied in the diagnosis of acute myocardial infarction (AMI). The most common approach for analysis includes RIA, IRMA, and electrophoresis, all of which may be time‐consuming. This study examines determination of CK‐MB and CK‐MB 2 by a rapid immunochemical extraction method followed by an automated measurement for both analytes. The automated method was sensitive to 2 U/L, linear to 180 U/L, and gave excellent interassay precision (<10% CV). Interference studies indicated that bilirubin, hemolysis, and lipemia caused analytical problems as did the presence of high activities of other CK isoenzymes, notably CK‐MM and CK‐BB, requiring dilution of samples prior to analysis. Application of immunochemical extraction gave a reference interval of CK‐MB (0–2.5 U/L) and CK‐MB 2 (0.1–1.4 U/L) for blood donors (20–60 years), peak levels for ruled‐out AMI patients of CK‐MB (0.5–7.3 U/L) and CK‐MB 2 (0.3–4.9), peak levels for ruled‐in AMI patients of CK‐MB (80–174 U/L) and CK‐MB 2 (80–155 U/L). Coronary artery bypass patients (n = 24) and all trauma patients (n = 14) also demonstrated elevations in CK‐MB and CK‐MB 2 , whereas only five of the trauma patients demonstrated increased CK‐MB by IRMA. In patients (n = 7) having increased total CK and normal CK‐MB by IRMA, the extraction assay for CK‐MB and CK‐MB 2 yielded increased values in all patients. This new approach to CK‐MB and CK‐MB 2 analysis can be performed within 30 minutes of sample receipt. J. Clin. Lab. Anal. 11:163–168, 1997. © 1997 Wiley‐Liss. Inc.