The comments made by Dr Cox are not necessarily in conflict with our original letter. We mentioned diffuse skeletal disorders, such as breast or prostate metastases, as the probable cause of the diminished renal uptake in the particular case in question. We have observed it on several occasions, as has Sy et al.1 It has proved quite useful. Unfortunately, Dr Cox has not observed it in diffuse skeletal disease as often as a number of other investigators have.
My co-authors and I did not wish to imply that diffuse skeletal disease was the only cause of the faint or absent kidney sign. Certainly, primary kidney failure is a major consideration. Additionally, some of Dr Cox's comments regarding the form of the technetium complex may provide another reason for decreased kidney concentration.
The important consideration is that the variation from the normal is appreciated. The cause of the