Comparison of bone and total alkaline phosphatase activity on bone turnover during menopause and in patients with established osteoporosis.

Abstract

Recently, a bone alkaline phosphatase (AP) enzyme immunoassay (EIA) was developed for measurement of bone AP activity with a monoclonal antibody. We compared the clinical performance of bone AP (bAP) measured by EIA and total AP (tAP) to examine if bAP is preferable to tAP as a bone formation marker in the post-menopause and established osteoporosis. Serum was obtained from 50 pre- and 93 post-menopausal healthy women, and 54 osteoporotic patients with vertebral fractures and 57 patients with hip fracture. Total AP was measured spectrophotometrically with p-nitrophenyl phosphate as substrate. The intra- and inter-assay coefficients of variation were 0.7-1.8% and 0.6-1.1%, respectively. Bone AP activity (bAP) was measured by EIA kit, ALKPHASE-B (Metra Biosystems, Inc.) using a monoclonal antibody against human bone AP. The intra- and inter-assay CVs were 4.0-8.3% and 6.2-7.9%, respectively. The percentage mean increase of bAP (54.9%) in post-menopausal subjects over premenopausal subjects was higher than that of tAP (40.1%). In age-matched comparison, % mean increases were 57.5% for bAP and 35.3% for tAP. Z-score for bAP in post-menopausal subjects was significantly higher than that for tAP. However, there was no significant difference in Z-scores between tAP and bAP in osteoporotic patients with vertebral fractures or with hip fracture. The correlation coefficient of bAP with age (r = 0.316) was similar to that of tAP with age (r = 0.319). In post-menopausal subjects, there was no difference in the concentrations of tAP nor bAP among the groups in whom times since the menopause was 0-9 years, 10-19 years and more than 20 years. Bone AP was highly correlated to tAP in the normal subjects, the patients and the total study group. Preference can be given to bone AP by enzymatic immunoassay over total AP based on their clinical utility during the menopause; however, no preference can be given to bone AP over total AP in established osteoporosis.