Biochemical markers of bone turnover are influenced by recently sustained fracture.

In striving to refine the clinical utility of different markers of bone metabolism, we should take into account numerous confounders, many of which are well known, such as sampling time, fasting status, and bone density. One further confounder may be ongoing fracture healing and/or post-fracture immobilization, which at least theoretically should impose an increased bone formation and resorption. Since both recent fracture and high bone turnover are independent predictors for new fracture, we thought it of importance to define the potential influence of such fracture on markers of bone turnover. From a population-based cohort of 1604 women, all 75 years old (the OPRA-study), 1024 women attended a clinical examination. The bone metabolism was assessed in serum, by three markers of bone formation [bone-specific alkaline phosphatase (S-Bone ALP), intact and N-Mid osteocalcin (S-Total OC), and total carboxylated osteocalcin (S-cOC)], two markers of bone resorption [C-terminal cross-linked telopeptides of type I collagen (S-CTX) and tartrate-resistant acid phosphatase type 5b (S-TRACP5b)], and in urine by one marker of bone resorption [deoxypyridinoline/creatinine (U-DPD/crea)] and two putative markers of bone resorption [urinary osteocalcins (U-OC/crea)]. Current physical activity and retrospective fracture data were recorded by questionnaires. The fracture data, for the entire cohort of 1604 women, were validated with radiographic referrals and reports, saved since the beginning of the last century. All data provided, except date of occurrence of retrospectively sustained fracture, were thus obtained cross-sectionally and in all women at the age of 75. Fracture had ever been sustained by 727 of the entire cohort (n = 1604), and by 523 of the attending women (n = 1024). All markers were marginally higher (significant only for U-DPD/crea, P = 0.027) in women who had ever sustained fracture, compared to women without fracture. In women with recent retrospective fracture (since 2 years) (n = 100), the levels of all markers, except the two S-OCs, were significantly higher (r = 0.20-0.33, P = 0.049-0.001) the more recently the fracture had been sustained. Women with low current physical activity had elevated levels of U-DPD/crea (P < 0.001) and one U-OC (P = 0.014), while the other markers were unaffected.