Differential effect of age, gender and puberty on bone formation rate assessed by measurement of bone-specific alkaline phosphatase in healthy Italian children and adolescents

Bones undergo intensive modeling during growth, a process involving both formation and resorption processes. Bone formation can be accurately monitored by measurements of bone-specific alkaline phosphatase (BAP) in serum. The lack of appropriate reference values has hampered the use of BAP in pediatric subjects. The purposes of the present study were to verify the effect of age, gender, and puberty on BAP concentration in healthy children, and to generate reference curves. Morning blood samples were collected from 239 healthy children and adolescents (113 boys), aged 4.5-20.9 years. Anthropometric measurements and pubertal stage were recorded. Blood samples were also obtained from 37 healthy young adults (13 men), aged 21.5-30.2 years. BAP concentration varied significantly with age, showing a peak at age 10-12 years in girls and 12-14 years in boys. Prepubertal concentration of BAP was six- to sevenfold higher than in healthy adults. We observed significantly higher BAP values at the beginning of puberty (stage II) compared to prepubertal stage in both sexes. The effect of puberty was independent from age and gender. We demonstrated that BAP serum concentration varies with age in children and adolescents, and we provided equations to calculate reference values. Because BAP concentrations vary markedly according to the pubertal stage, the values of BAP obtained in single patients should be compared to reference considering not only age and sex, but also the stage of pubertal development.