An improved method for the determination of creatine kinase activity in serum

An improved method for the determination of creatine kinase activity (EC 2.7.3.2) is described. For the reactivation of creatine kinase serum is first preincubated in the test solution in the presence of dithioerythritol. Then the enzymatic reaction is started by adding creatine phosphate. By optimizing the concentrations in the test solution and by altering the measurement procedure using dithioerythritol as reactivator, the assay is made more sensitive, and a far higher enzyme activity in serum is measured in comparison with other recommended tests. The reaction rate is linear for ten minutes up to 700 U/l. An increase in activity by enzyme dilution was not observed. In this study a sensitivity of detection of 0.9 U/l was achieved. This would be especially advantageous in the detection of the isoenzymes of creatine kinase after chromatography. Within-run precision was 1.2% (CV), day-to-day precision was 2.0% (CV). The test solution is stable for at least 24 hours.