Influence of renal function on renal output efficiency.

Abstract

The purpose of this study was to quantify the influence of renal function on output efficiency (OE) and to evaluate factors that may modify this effect. Renograms were generated in a computer simulation model by convolution of plasma disappearance curves with artificially created retention functions. Ten plasma curves were derived from a database corresponding to renal clearances ranging from 33 to 405 mL/min. The created retention functions had 3 characteristics: (a) no output until the minimal transit time (MinTT) followed by a linear increase in transit time; (b) ratio of MinTT to mean transit time (MTT) equal to 0.3 or 0.8; and (c) MTT between 3 and 60 min, increasing with 1-min steps. For each of the 1,160 renograms generated, output efficiency at time (t), OE(t), was calculated at 20, 40, and 60 min. Mean and SD of OE(t) for all clearances were calculated for MTT values between 5 and 60 min, increasing with 5-min steps. For the same retention function, different clearances resulted in different values of OE(t). The degree of variability of OE(t) depended on several factors, including the value of t, the value of MTT, and the shape of the retention function, expressed as the MinTT-to-MTT ratio. For OE(20), OE(40), and OE(60), the respective maximum SDs were 5.4%, 6.6%, and 7.1% for retention functions with a MinTT-to-MTT ratio equal to 0.3, and 6.2%, 8.4%, and 9.4% for retention functions with a MinTT-to-MTT ratio equal to 0.8. OE is influenced by renal function. Care should be taken in establishing the cutoff values for obstruction, non-obstruction, and the nondiagnostic zone, since a change in overall clearance can cause as much as a 20% variation in OE.