An improved procedure for serum creatine phosphokinase determination.

Abstract The creatine phosphokinase activity of serum is determined by a procedure in which adenosine triphosphate, liberated by the action of the enzyme, is linked to the reduction of nicotinamide-adenine dinucleotide phosphate and the formation of reduced nicotinamide-adenine dinucleotide phosphate followed spectrophotometrically. The enzyme substrate for the reaction is prepared in bulk, freeze-dried, and distributed in gelatinecovered capsules. The capsule contents are reconstituted immediately before use by the addition of distilled water, and creatine phosphokinase activity is determined by measuring the increase in optical density at 340 mμ following serum addition. The method is convenient, more sensitive, and less time-consuming than other procedures for serum creatine phosphokinase determination in common laboratory use.