Factors influencing the accuracy of renal output efficiency.

Output efficiency (OE) has been proposed as an objective tool for the estimation of renal emptying. The aim of this paper was to evaluate some factors that may affect the value of this parameter obtained by a 99Tcm MAG3 renogram. In 22 patients, the effect of different types of renal background correction was calculated. In 10 patients, simultaneous gamma camera renography and multiple blood sampling allowed the error of using a heart curve instead of a plasma curve to be evaluated. Finally, an evaluation was carried out on the effect of neglecting the change of plasma activity between the end of the furosemide acquisition and the post-micturition view obtained after repositioning of the patient on the gamma camera: 142 patients who had had multiple blood sampling were retrospectively selected for that purpose. It has been shown that all these factors may significantly affect the value of OE, particularly in cases with poor renal drainage. Unless standardization of the procedure is introduced for some of these factors, the cut-off levels for good, fair and poor drainage may vary between centres.