Noninvasive estimation of kidney function by x-ray fluorescence analysis: biological half-time and clearance of contrast material in rabbits.

A noninvasive method for glomerular filtration rate-determination, in which the use of radioactive tracers and sampling of plasma and urine can be omitted, is described. After injection of iodinated contrast material in rabbits, the iodine content of tissue, serum, and urine is measured by means of x-ray fluorescence analysis. The disappearance rates of iodine in tissue and serum are found to be the same, and a strong correlation is found between clearance values calculated from serum and tissue measurements. This indicates the possibility of evaluating kidney function by x-ray fluorescence analysis of contrast material in tissue only.