Biochemical Markers of Bone Turnover

Abstract

The routine clinical assessment of bone mineral density (BMD) is best undertaken by the use of dual-energy X-ray absorptiometry (DXA) and ultrasound scans. These techniques will establish BMD at a particular time. Using serial DXA measurements it is possible to measure a change in BMD over a set period of time. It is presumed that these measured changes in BMD are caused by alterations in bone turnover, but they are not direct measurements of bone turnover. Furthermore, DXA scans and ultrasound can only indicate that loss of BMD has occurred, a single measurement cannot indicate that bone loss is occurring, and might lead to a lowered BMD in the future. These radiological and ultrasound techniques have other limitations, not least inherent imprecision of the methods, which means that there have to be considerable changes in bone turnover before changes in BMD can be noticed. For example, the 1–2% imprecision of DXA measurement limits scanning to 6-monthly intervals, so that observed changes are certain to be owing to bone loss and not imprecision. The skilled nature of these techniques combined with the need for special equipment, and in the case of DXA exposure to ionizing radiation, has fueled the search for useful and reliable markers of bone turnover.