COMPARISON OF TOTAL ALKALINE-PHOSPHATASE AND 3 ASSAYS FOR BONE-SPECIFIC ALKALINE-PHOSPHATASE IN CHILDHOOD AND ADOLESCENCE

We compared serum levels of total alkaline phosphatase (TAP) and bone- specific alkaline phosphatase (BAP) as determined by three different a ssays (lectin affinity electrophoresis, immunoradiometric assay, enzym e-linked immunosorbent assay) in subjects aged 5-20 years suffering fr om X-linked hypophosphatemic rickets (n = 14), chronic renal failure ( n = 10) and chronic cholestatic liver disease (n = 16). Results were c ompared to controls of the same age and were expressed as standard dev iation scores (SDS). TAP correlated significantly with BAP (r > 0.9 fo r each assay; p < 0.001) in controls. In children with cholestatic dis eases, TAP (median SDS + 2.0) was elevated, but BAP, as measured by th e electrophoretic assay, was within the reference range for most patie nts (median SDS: -0.4; p = 0.003 for the difference between the median SDS of TAP and BAP). In contrast, results for BAP as determined by th e two immunoassays were not significantly different from TAP in any of the three patient groups (p > 0.05 in each group for both assays). In this study, the two immunoassays did not have a detectable advantage over lectin affinity electrophoresis in the determination of BAP.