The utility of alkaline phosphatase measurement as a screening test for rickets in breast-fed infants and toddlers: a study from the puget sound pediatric research network.

To determine if alkaline phosphatase (AP) levels are a useful screening test for rickets, the authors measured serum AP levels in children 6 to 15 months old who were predominantly breast-fed for > 6 months without vitamin D supplementation. Radiographs were obtained on children with elevated AP levels to determine the presence of rickets. AP levels were obtained on 246 children; levels were elevated in 33 (13.4%). Rickets was present in 4 of 18 children with elevated levels on whom radiographs were obtained. The sensitivity and specificity of AP levels as a test for rickets was maximal at a cutoff value of 552 U/L. Using this cutoff value, the specificity of AP levels as a test for rickets was 97.4%, and the positive predictive value (PPV) was 40.0%. These results suggest that AP levels may be a useful screening test for rickets in children who are breast-fed for prolonged periods without vitamin D supplementation.