A simple method for estimating the skeletal uptake of diphosphonates.

It is possible to obtain an estimate of the bone uptake of diphosphonates after 3 h (BU) on the basis of the difference between the dose administered and the sum of the component eliminated in the urine plus the component present in the extra-osseous volume of distribution. The results of this simple method have been compared in 15 patients using whole body retention at 24 h (determined by means of a complete urine collection) and the ratio of plasma concentrations of 51 Cr-EDTA/ 99 Tc m -HMDP after 3 h (DPS). Both DPS and BU can be used on a practical basis, and therefore be used routinely with scintigraphy. The added advantage is that, for BU, the use of a second radiopharmaceutical is avoided.