The Performance and Utility of Biochemical Markers of Bone Turnover: Do We Know Enough to Use Them in Clinical Practice?

Several new biochemical techniques to assess bone turnover have been developed over the last decade. I These techniques are divided into those which are believed to reflect either the rate of bone formation or the rate of bone resorption (Table I). The validity of marker of bone turnover can be considered in different ways (Table 2). The distinction between these different aspects of validity is important, because it leads to rather different interpretations of what is meant by a valid test. Markers of bone turnover are clearly useful in population-based epidemiological studies, and in therapeutic research studies. However, the routine clinical use of these measurements has been enthusiastically advocated, despite uncertainty about exactly how they should be used, or whether they can be relied upon to provide useful information in clinical practice. In any particular clinical context, it is necessary to decide: (I) which analyte to measure; (2) how to measure it; (3) when to measure it; (4) how the sample should be collected; and (5) how to interpret the result. To assess the clinical validity of markers of bone turnover, we need a clear understanding of exactly what information the measurements are intended to provide. Although traditional markers of bone turnover (total alkaline phosphatase, tartrate resistant acid phosphatase and hydroxyproline) are non-specific indicators of bone turnover, they may be as reliable as more specific measurements when bone turnover is markedly elevated, as in severe Paget's disease of'bone.? The