Quantification of skeletal alkaline phosphatase in osteoporotic serum by wheat germ agglutinin precipitation, heat inactivation, and a two-site immunoradiometric assay

Three methods for quantifying skeletal alkaline phosphatase (ALP; EC 3.1.3.1) activity/immunoactivity in serum-heat inactivation, wheat germ agglutinin (WGA) precipitation, and an immunoradiometric assay-were tested for recovery and specificity and applied to 81 sera collected from 14 postmenopausal osteoporotic subjects. The heat-inactivation and WGA precipitation assays showed relative recoveries of 91-100% and 16-32%, respectively, for skeletal ALP with complete specificity (no cross- reactivity with hepatic or intestinal ALP); the IRMA showed a relative recovery of 86-100% and 11-14% cross-reactivity with hepatic ALP. There was a closer correlation between the heat-inactivation assay and IRMA (r = 0.833) than between the WGA precipitation assay and IRMA (r = 0.673) or between the heat-inactivation and WGA-precipitation assays (r = 0.568). The WGA precipitation assay failed to detect skeletal ALP in three serum samples that contained significant amounts as determined by the heat-inactivation assay and the IRMA.