MONOCLONAL-ANTIBODY ASSAY FOR MEASURING BONE-SPECIFIC ALKALINE-PHOSPHATASE ACTIVITY IN SERUM

Alkaline phosphatase (ALP) is present in human serum in the form of se veral isoenzymes. The two major circulating ALP isoenzymes, bone and l iver, are difficult to distinguish because they are the products of a single gene and differ only by posttranslational glycosylation. Quanti tative measurement of bone ALP (BAP) activity in serum can provide an index for the rate of bone formation. Furthermore, increased BAP activ ity in serum is indicative of bone disorders, We describe a method in which serum samples are added to a microtiter plate coated with monocl onal anti-BAP antibody and incubated 3 h at room temperature. After th e unbound materials are washed off, the bound BAP activity is measured by adding p-nitrophenyl phosphate substrate. The assay demonstrated n o cross-reactivity to intestinal or placental ALP and only 3-8% cross- reactivity to liver ALP. The intraassay (n = 21) CVs were 3.9-5.9%, an d interassay(n = 8) CVs were 4.4-7.0%. Comparisons of the assay (y) wi th an IRMA (x) and a wheat germ agglutinin precipitation method (x') g ave regression equations of y = 1.32x - 6.4, r = 0.99, and y = 1.41x' + 4.8, r = 0.99. The assay detected increased BAP in sera from patient s with osteoporosis, Paget disease, osteomalacia, or primary hyperpara thyroidism.