Prevalence of transient hyperphosphatasemia among healthy infants and toddlers

To describe the prevalence and clinical characteristics of transient hyperphosphatasemia (TH) in a cohort of healthy infants and toddlers.

We performed a secondary data analysis of healthy infants and toddlers enrolled in a study examining the epidemiology of vitamin D deficiency. From 2005 to 2007, children aged 8 to 24 months were enrolled during well-child visits at an urban primary care pediatric clinic. At enrollment, we collected data regarding sociodemographic and clinical characteristics. We measured serum levels of alkaline phosphatase (AP), 25-hydroxyvitamin D, parathyroid hormone (PTH), calcium, magnesium, and phosphorus. We placed participants into 1 of 3 categories on the basis of serum AP levels: normal (AP: 110-400 U/L), intermediate (AP: >400 to 1000 U/L), and TH (AP: >1000 U/L). We used Fisher's exact test and analysis of variance to evaluate differences in characteristics among the 3 groups.

Nine (2.8%) of 316 children had an AP level of >1000 U/L (mean: 2165 U/L). Sixteen children (5.1%) had an intermediate serum AP level (mean: 544 U/L). Mean weight-for-age, length-for-age, and weight-for-length z scores were similar across all 3 AP groups. Compared with the 291 children without TH, children in the intermediate AP and TH groups had similar mean serum levels of 25-hydroxyvitamin D, PTH, calcium, magnesium, and phosphorus.

TH seems to be a relatively common condition among healthy infants and toddlers. TH was not associated with anthropometric measures, vitamin D status, PTH, or serum minerals. Recognition of this benign condition is important to avoid unnecessary investigations.