Urinary 99m-Tc-diphosphonate excretion as a simple method to quantify bone metabolism

Twenty-four-hour whole-body retention (WBR) of 99m-Tc-methylene-diphosphonate (an index of bone turnover) was determined by whole-body counting (WBRs) and complementarily by urine counting (WBRu) in nineteen subjects with normal to highly increased bone turnover. WBRs and WBRu correlated well (r = 0.94, P less than 0.001), and gave almost the same results. Both WBRs correlated equally well with serum alkaline phosphatase and urine hydroxyproline/creatinine (r = 0.82-0.93). Coefficient of variation in WBRu was 7.0%, determined by duplicate measurements in sixteen normals. The injected dose of diphosphonate did not influence WBRu. However, since almost 50% of the diphosphonate excreted in urine appeared during the first few hours after the i.v. injection, the method of WBRu requires careful urine collection. Thus, the simple WBRu determination provides the same information on bone metabolism as does the more cumbersome and expensive WBRs technique.