Does radiolabelled diphosphonate retention reflect bone metabolism in the elderly?

The 24-h whole-body retention of diphosphonates (WBR), a useful measure of bone metabolism in young subjects, was measured in 27 elderly subjects (19 from home and eight in-patients). WBR rose with increasing age (r = 0.55, P less than 0.01) and was negatively correlated with renal function (r = -0.60, P less than 0.01). In five subjects given vitamin D, WBR did not fall. The measurement of WBR in the elderly has to be assessed in the light of an accurate assessment of renal function and so is rarely clinically useful.