Creatine kinase isoenzyme MB determination on the ACA: dependence on serum matrix and other effectors.

Creatine kinase isoenzyme MB catalytic activities in human serum, determined by ACA ion exchange chromatography and immunoinhibition, differ significantly, the correlation coefficient being 0.88. The reasons for this variation are interference of antibodies with the creatine kinase B subunit in the immunoinhibition assay, nonreproducible elution of creatine kinase isoenzyme MB from the ion exchange resin in the ACA pack, due to varying protein concentrations in the serum samples and increasing elution of creatine kinase isoenzyme MM from the ion exchange column caused by a preceding partial inactivation of creatine kinase isoenzyme MM. Pretreatment of serum samples with a solution containing magnesium sulphate, maleate and 2-oxoglutarate (solution A) prior to determination of creatine kinase isoenzyme MB catalytic activities on the ACA significantly improves the sensitivity and specificity of the method; the correlation coefficient for the values from the ACA and immunoinhibition then becomes 0.92. Dilution of serum samples with bovine serum albumin solution is now practicable.