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Abstract |
Standardization Trial of Biochemical Markers of Bone Turnover |
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Biochemical markers of bone metabolism are widely used to assess patients with metabolic bone disease. However, variability of those markers and the need for standardization has been an issue of practical concern. We here report on the results of a proficiency testing program for biochemical markers of bone metabolism amongst clinical laboratories in Europe. The trial was announced in early 1999 through various media. Of the 113 laboratories responding, 78 commercial or public institutions were eligible. Testing materials were two serum and two urine pools with low and high marker concentrations, respectively. Each laboratory received 1 aliquot of both pools on dry ice. Samples had to be analyzed within two weeks of receipt. Results were analyzed by univariate descriptive statistics and Youden-Plots. Measurement of urinary PYD and DPD by HPLC showed the expected high degree of variability due to use of different methods and standards. However, most commercial immunoassays also exhibited a large range of variability with CVs between 6 - 38.8%. Thus, within the same sample, results for identical marker components may differ up to 5.6-fold. Creatinine normalization as a rule leads to higher variability in most assays. We conclude that in order to reduce analytical variability, further standardization of bone marker assays is needed. This could be chieved by the introduction of international standards (e.g. HPLC), by minimizing lot-to-lot-variation in immunoassays, and by the development of reference methods for bone marker assays and possibly for urinary creatinine. Bone marker assays should be included into laboratory proficiency programs. |
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