Age-related reference intervals for creatine kinase BB in serum.

The mass concentration of creatine kinase BB (CK-BB) isoenzyme was measured in serum of 365 healthy children and adults with a CK-BB specific radioimmunoassay. Eight separate age groups (newborns, 4 days, and 1, 8, 14, 25, 40 and 65 years) were examined and the reference intervals for these groups were estimated. The concentration of CK-BB generally decreased with increasing age, most of the changes taking place within the first year of life. Thus, the median value at age 1 year (9.2 micrograms/l) was 1/15th of that observed at birth, 1/2 of that observed at age 4 days, but four times higher than that observed in adults. A transient increase in CK-BB concentration was observed in boys 14 years old. At this age in contrast to at all other ages the values measured in boys were significantly (P less than 0.005) higher than the values measured in girls In 27 of the sera from cord blood we also examined the relationship between estimates of CK-BB mass and activity, the latter being estimated by immuno-inhibition technique. The two estimates were highly correlated (r = 0.98), 2 micrograms of enzyme mass roughly equivalent to 1 U of enzyme activity.