Bioluminescence assay of creatine kinase and its isoenzymes in serum and cerebrospinal fluid.

Abstract

Abstract We examined the sensitivity of bioluminescence for the determination of very low concentrations of creatine kinase brain-type subunit (CK-BB) in serum and in cerebrospinal fluid. To optimize the sensitivity of CK-isoenzyme assays and eliminate possible sources of error, we separated the isoenzyme fractions by using inhibiting anti-MM and precipitating anti-MM and anti-BB antibodies. The results with the bioluminescence assay correlated with spectrophotometric values such that r = 0.97 for the total CK activity and r = 0.98 for the CK-B activity. The reproducibility of the present method was comparable with the spectrophotometric method and was even better at low enzyme activities. The within-series precision for assay of total CK activity at 2 U/L corresponded to a CV of 9%; at 13 U/L the CV was 5.8%. All the assays were carried out at 25 degrees C. Even at this low temperature, CK activities as low as 0.2 U/L could be determined. In eight patients without any evidence of cerebral cell damage, total CK activity in cerebrospinal fluid was x = 1.05 +/- 0.6 U/L, and CK-BB activity was x = 0.7 +/- 0.4 U/L. In sera of these patients CK-BB activity was x = 0.6 +/- 0.5 U/L. Differences in CK and CK-BB activities in four patients with transient or progressive brain-cell damage are discussed.