Bone turnover and its relationship with bone mineral density in pre- and postmenopausal women with or without fractures

Objective: This work was carried out in order to investigate possible relationships between bone turnover rate, as evaluated by bone biomarkers and skeletal mass, as evaluated by bone mineral density (BMD). Method: Fifty-eight normal women and 30 female patients with osteoporotic fractures were enrolled. Three groups were defined: (1) fertile subjects (n=24), mean age 33.7±8.1 years; (2) postmenopausal women (n=32, including 11 patients with fractures) whose BMD values, in terms of T score, were less than −2.5 S.D. below the young adult mean obtained in our laboratory (mean age 61.7±7.9 years; and years since menopause (ysm), 12.6±8.3); (3) postmenopausal women (n=32, including 19 patients with fractures) whose BMD values in terms of T score, were below −2.5 S.D. (mean age 62.9±8.6 years; and ysm 15.9±9.0). Groups II and III characterised, by inclusion criteria, by significant different mean BMD values, were similar as far as chronological and menopausal age were considered. Metabolic tests included a short urine collection to determine calcium, hydroxyproline, cross-linked N-telopeptides of type I collagen (NTx) and creatinine (Cr); half-way through this collection, a blood sample was taken for the measurement of total alkaline phosphatase activity (ALP) and tartrate-resistant acid phosphatase activity (TRAP). BMD at lumbar spine was evaluated. Results: There were significant differences amongst the three groups in mean ALP (P<0.001, by analysis of variance) TRAP (P<0.006) and NTx/Cr (P<0.001) values, but not as far as mean values of calcium/Cr or hydroxyproline/Cr ratios were concerned. Considering the group as a whole, there were significant inverse correlations between NTx/Cr, ALP, TRAP and BMD controlling for both age (r=−0.392, P<0.001; r=−0.447, P<0.001 and r=−0.327, P<0.002, respectively) and ysm (r=−0.374, P<0.001; r=−0.474, P<0.001 and r=−0.333, P<0.002). Conclusions: Our results indicate, that, even after controlling for both ageing and oestrogen status, there is an inverse relationship between bone mass (that at a given time represents the balance of all previous metabolic events) and a biochemical marker (which reflects bone turnover at the time of examination). These findings are in line with the belief that increased bone turnover should be regarded as a risk factor for osteoporosis. Furthermore, our results indicate that, unless there is no increase of hepatic isozyme, total ALP still maintains a possible role as a first analysis to evaluate bone turnover before requesting markers with greater specificity, sensitivity but also more expensive and whose analysis is sometimes time-consuming.