Bone Gla protein (osteocalcin) assay standardization report.

The major conclusion of this study is that the different laboratory assays for serum BGP give a reasonably consistent picture of bone metabolism in the metabolic bone diseases examined only if the results are expressed as a percentage of serum BGP levels in normal individuals. This requires that all laboratories establish a mean control serum BGP value in an appropriate population of normal individuals. Since BGP levels determined by different laboratories on the same serum sample can vary by more than fourfold, the absolute serum BGP levels determined in one laboratory cannot be compared directly with the serum BGP levels determined in another. Although we cannot comment on the efficacy of different laboratory assays for serum BGP as measures of bone metabolism in disease states that were not examined, such as osteoporosis, it is clear that the large differences between laboratory assays make it imperative that all interlaboratory comparisons be based on values expressed as a percentage of serum BGP in an appropriate population of normal individuals.