During a study carried out at the Montreal Children's Hospital involving measurement of serum creatine phosphokinase (CPK) levels in healthy children, it was found that some teenaged boys had elevated values. We then studied a group of teen-aged children at least five times over a seven-week period to estimate the normal intrapatient and interpatient variation in CPK levels. There was no restriction of sporting activities.
The results are summarized in the Table. The girls were active in sports (basketball and gym), but none of their values fell outside the normal range for our laboratory (0 to 108 international units [IU]). (Details of methodology available on request.) Their mean value (59 IU) was comparable to a larger multi-aged control group. Seventeen of the 28 values obtained in boys were elevated, and two boys had consistently elevated determinations. Although no quantitative measurement of exercise was made, it was not possible to