Standardization of creatine kinase-MB (CK-MB) mass assays: The use of recombinant CK-MB as a reference material

Background: The AACC assembled a committee to identify and validate a stand ard creatine kinase MB isoenzyme (CK-MB) material to improve the comparabil ity of CK-MB mass assays. Methods: Three protocols were used. In protocol I, various CK-MB materials prepared in different matrices were screened as candidate standards. In pro tocol II, participating manufacturers calibrated their systems with concent rates of human heart CK-MB and then tested 20 patient samples to evaluate c alibration bias. In protocol III, participating manufacturers calibrated th eir immunoassay systems using recombinant CK-MB2 (rCK-MB2) diluted into the ir respective sample diluents and measured 50 samples. Results: Candidate materials showed high recovery in stripped human serum, but bias improved only from 59% to 38%. These data led to the use of human heart CK-MB diluted in each manufacturer's sample diluent. This strategy re duced bias from 31% to 15%. Because human heart CK-MB is difficult to provi de, a lyophilized source of CK-MB2 was identified, rCK-MB2 was shown by sod ium dodecyl sulfate-polyacrylamide gel electrophoresis, reversed-phase HPLC , intrinsic protein fluorescence, circular dichroism, agarose gel electroph oresis, immunoreactivity studies, high and low temperature stability, and r econstituted stability to be equivalent to human heart CK-MB. Calibration o f immunoassay systems with rCK-MB2 added into each respective manufacturer' s sample diluent showed a 13% between-manufacturer bias. Conclusion: Lyophilized rCK-MB2 was determined suitable for use as a refere nce material for CK-MB mass assays. (C) 1999 American Association for Clini cal Chemistry.