Role of bone density and biochemical markers of bone turn-over in the 'prediction' of bone loss and bone fracture

Since risk factors for osteoporosis allow an estimation of the probability of future fractures, risk factors are said to have a 'predictive' ability for the occurrence of fractures. This terminology must be put in its proper probabilistic perspective. Risk factors for fracture predict the probability of fracture, but cannot identify individuals who will have a fracture. Nonetheless, even if a prediction does not come true in an individual patient, it will usually be borne out in many such cases. Therefore probabilities based on risk factors can guide clinical decision making. Bone density is considered the most important predictor of osteoporotic fragility fractures. Most measuring sites have virtually the same predictive ability for a decrease of 1 SD in bone density. However, measurement at the spine seems better for spine fractures, while measurement at hip appears better for predicting hip fracture. The role of ultrasonographic parameter of bone at calcaneous is promising, especially in elderly women, but needs to be further confirmed. Biochemical markers of bone turnover provide little value in the diagnosis of osteoporosis but some groups have shown in recent prospective studies that these indices may provide an estimate of fracture risk, independently of bone density, and that the combination of BMD measurements and biochemical markers might provide a better definition of the risk of fracture. The relationship between biochemical markers and rate of bone loss in early postmenopausal women is still controversial.