Measurement of relative renal function. A comparison of methods and assessment of reproducibility.

A good correlation was found between relative uptake of 99Tcm dimercaptosuccinic acid (DMSA) and relative 131I orthoiodohippuric acid clearance in a group of 100 consecutive patients without evidence of renal failure. In the majority, attenuation correction was found to make no significant difference to relative function measurement. Those in whom it did could be readily identified by inspection of the posterior DMSA images at the time of examination. Two hundred patients were reviewed in whom serial studies had been performed over the previous 5 years. Differences in relative function greater than 5% indicated a high probability that a real change in renal function had occurred. We conclude that whilst renography and DMSA scintigraphy yield complementary information, relative function (L/L + R) can be measured equally well by either method, and the results are sufficiently reproducible to be clinically useful.