Measurement of bone-specific alkaline phosphatase by an immunoselective enzyme assay method.

We evaluated a new immunoselective enzyme assay of bone-specific alkaline phosphatase (ALP). The monoclonal antibody used in this assay was raised against purified bone-specific ALP obtained from SAOS-2 human osteosarcoma cell line. Calibration was based on the enzyme's own activity. The relative activity of the antibody was 100% with bone ALP, 8.7% with liver ALP, and 0% with placental and intestinal ALPs. Intra- and inter-assay coefficients of variation were less than 4%. The sensitivity of the assay was 0.7 U/L, and the linearity extended from 2 to 140 U/L. The recovery of bone-specific ALP standard added to serum was 94-106%. The correlation coefficient between this method and the polyacrylamide 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 activities in 60 premenopausal women (mean age 39 years, SD 8 years) and 70 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 women (P < 0.01). We conclude that this new immunoassay of bone-specific ALP would be useful for clinical investigation of patients with osteoporosis or other metabolic diseases of bone.