Biochemical markers in bone diseases

Abstract

Bone remodelling is a tightly regulated process which occurs throughout adult life. The process consists of two main steps: bone resorption and bone formation phase. During these two phases, several breakdown products of bone matrix including C-terminal or N-terminal telopeptide of type 1 collagen (CTX, NTX) and collagen crosslinks (deoxypyridinoline, pyridinoline) as well as components involved in bone formation such as collagen type 1 propeptides, osteocalcin or enzymes (bone-specific alkaline phosphatase), are released in the circulation. These products can be measured and used clinically as biochemical markers to assess bone turnover rate. They provide a useful and non-invasive tool in the investigation and follow-up of patients with post-menopausal osteoporosis and other skeletal disorders. However, their variability presents a problem to their establishment in routine practice. Identifying the factors which contribute to this variability, the degree of variability and taking steps to minimise these such as standardisation of the assays and timing of sample, as well as the derivation of well-defined reference ranges, would improve the clinical utility of these bone markers in individual patients. The clinical uses of the biochemical markers of bone turnover are reviewed. Their role in the prediction of fracture risk and the assessment of treatment response in post-menopausal osteoporosis is described. The potential use of the markers in metastatic bone disease is also discussed.