Results of a nationwide survey of analyses for creatine kinase and creatine kinase isoenzymes.

More than 300 laboratories participated in an interlaboratory survey of creatine kinase (CK, EC 2.7.3.2) determinations in which they analyzed seven lyophilized samples for total CK and CK isoenzymes and furnished information about their methodology. The samples were not necessarily intended to mimic typical patients' specimens but rather to determine the analytical ability of the laboratories to distinguish isoenzyme fraction CK-MB from CK-BB and to detect small but abnormal amounts of CK-BB. For total CK measurement, most laboratories used an NADP+ reduction method monitored at 340 nm (89%), and reported results in units per liter (U/L) (99%) at either 30 degrees C (34%) or 37 degrees C (60%). Despite the variety of analytical conditions, most laboratories (89%) correctly reported results within their normal range for all samples. The 287 laboratories that reported isoenzyme distributions in the samples used either cellulose acetate (37%) or agarose (44%) electrophoresis, ion-exchange chromatography (9%), or immunoinhibition (7%). Results from laboratories that used nonspecific CK-MB immunoinhibition techniques were biased when a significant amount of CK-BB isoenzyme was present.