[Clinical use of biological markers of bone turnover in osteoporosis].

Osteoporosis is "a systemic bone disease characterized by a decreased bone mass and altered bone architecture resulting in an increased propensity to fracture". It results from a rather long evolution where in most cases bone resorption is increased, and is not compensated by an equally increased bone formation. Besides the effect of this negative balance on bone mass, the increased resorption results in an increased cortical porosity and in trabecular perforations which alter bone resistance. The measurement of the apparent bone density (BMD) on which relies the diagnosis of osteoporosis cannot alone describe this situation. The measurement of the biochemical markers of bone turnover allows completing the picture; these markers appeared indeed as independent risk factors for fracture, independently of the BMD. Moreover, they allow following the early effects of treatments aiming to decrease bone resorption or to increase formation. This follow up is interesting because it allows controlling the treatment efficacy, which can be hampered by a low compliance. It allows also to predict the effect of treatment in terms of bone gain and fracture risk reduction, and to encourage the patient to persist with the treatment in the long run.