MEASUREMENT OF BONE-SPECIFIC ALKALINE-PHOSPHATASE BY AN IMMUNOSELECTIVE ENZYME ASSAY-METHOD

We evaluated a new immunoselective enzyme assay of bone-specific alkal ine phosphatase (ALP). The monoclonal antibody used in this assay was raised against purified bone-specific ALP obtained from SAOS-2 human o steosarcoma cell line. Calibration was based on the enzyme's own activ ity. The relative activity of the antibody was 100% with bone ALP, 8.7 % with liver ALP, and 0% with placental and intestinal ALPs. Intra- an d inter-assay coefficients of variation were less than 4%. The sensiti vity of the assay was 0.7 U/L, and the linearity extended from 2 to 14 0 U/L. The recovery of bone-specific ALP standard added to serum was 9 4-106%. The correlation coefficient between this method and the polyac rylamide gel (PAG) electrophoretic method was 0.94. The mean value of bone-specific ALP in 89 healthy adults (mean age 29 years, SD 5 years) was 18.5 U/L (SD 4.1 U/L). Interestingly, mean bone-specific ALP acti vities in 60 premenopausal women (mean age 39 years, SD 8 years) and 7 0 postmenopausal women (mean age 57 years, SD 5 years) were 20.3 U/L ( SD 6.5 U/L) and 31.1 U/L (SD 11.1 U/L), respectively. The age-related increase in bone-specific ALP was significant and more pronounced in w omen (P<0.01). We conclude that this new immunoassay of bone-specific ALP would be useful for clinical investigation of patients with osteop orosis or other metabolic diseases of bone.