Alkaline Phosphatase in Healthy Children: Reference Intervals and Prevalence of Elevated Levels

Abstract

Background: Transient hyperphosphatasemia (TH) is an often unnoticed benign entity, primarily affecting children below 5 years of age. However, the prevalence among healthy children is unknown. We used data from a Swedish pediatric reference interval project to estimate the prevalence of high alkaline phosphatase (ALP) among healthy children and to calculate pediatric reference intervals. Methods: Blood was collected from 699 subjectively healthy children aged 6 months to 18 years. After exclusion of subjects with high ALP, age- and gender-specific reference intervals were calculated. Results: Six children had ALP levels >16.7 µkat/l (>1,000 U/l), including 4 females and 2 males aged 7-22 months. The prevalence in the age group from 6 months to 2 years was 6.2% (6/97). None of the older children had levels of ALP >16.7 µkat/l. The study did not include the follow-up of these apparently healthy children. Consequently, conditions others than TH explaining the elevated ALP could not be excluded. However, general chemistry analyses, such as liver enzymes, calcium, intact PTH and vitamin D, were essentially normal in these children. Conclusions: The prevalence of high ALP among subjectively healthy children was approximately 2.4% below 5 years of age and 6.2% below 2 years. Reference intervals vary with age and gender.