Age dependence of serum enzymatic activities (alkaline phosphatase, aspartate aminotransferase, and creatine kinase) in healthy children and adolescents.

The activities of alkaline phosphatase, aspartate aminotransferase and creatine kinase in sera of 1,033 children and adolescents aged 5 to 20 years were measured. The results showed significant deviation from the gaussian distribution. Because of differences between sexes and nonlinear relationship to age, sex- and age-related values for the 95th, 90th, and 5th percentiles are presented. Alkaline phosphatase activity increased markedly between 5 and 14 years of age in male subjects and 5 and 12 years of age in female subjects. The peak at puberty was more pronounced in boys than in girls. After puberty, activities decreased toward adult values. Aspartate aminotransferase activity showed a gradual significant decrease between 5 and 17 years of age in male subjects and 5 and 16 years of age in female subjects; then it remained steady until 20 years of age. Creatine kinase activity remained constant in male subjects between 5 and 12 years old, then rose to a maximum at 15 to 16 years of age before declining rapidly toward adult values. In female subjects, creatine kinase activity remained stable from 5 to 12 years of age, then decreased gradually in early adulthood.