NORA: A simple and reliable parameter for estimating renal output with or without frusemide challenge

The aim of this study was to evaluate a simple parameter describing renal o utput, namely NORA (normalized residual activity). We first compared, in a simulated model, different parameters of transit to an ideal standard; we t hen compared, in a clinical study, NORA and output efficiency. I-123-hippur ate, Tc-99(m)-DTPA and Tc-99(m)-MAG3 plasma curves, each with two levels of renal clearance, were convoluted by means of different types of simulated retention functions, with different mean transit times. On the reconstructe d renograms, several parameters reflecting renal transit were determined an d compared with mean transit time. In a second step, in 33 patients, we com pared output efficiency and NORA (i.e. the residual renal activity), normal ized by the renal activity at 2 min. These two parameters were calculated a t the end of the renogram, at the end of the frusemide test and after the m icturition phase. In the simulated model, both output efficiency and NORA w ere only slightly influenced by the level of overall renal function. In the clinical study, a good correlation was found between output efficiency and NORA, whatever part of the study considered (renogram, frusemide test, pos t-voiding image). NORA is a simple and reliable parameter that allows quant ification of renal output; it is almost independent of the level of renal f unction and can be used whatever the timing of the frusemide injection. (C) 2000 Lippincott Williams & Wilkins).