QUANTIFICATION OF SKELETAL ALKALINE-PHOSPHATASE IN OSTEOPOROTIC SERUMBY WHEAT-GERM-AGGLUTININ PRECIPITATION, HEAT INACTIVATION, AND A 2-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 t ested for recovery and specificity and applied to 81 sera collected fr om 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 cros s-reactivity with hepatic or intestinal ALP); the IRMA showed a relati ve recovery of 86-100% and 11-14% cross-reactivity with hepatic ALP. T here 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 AL P in three serum samples that contained significant amounts as determi ned by the heat-inactivation assay and the IRMA.