ABSTRACTS PRESENTADOS AL 11th INTERNATIONAL SYMPOSIUM "RADIONUCLIDES IN NEPHRO-UROLOGY", REALIZADO EN MONTEREY, CALIFORNIA, 13-17 MAYO 2001.

8. CAN DMSA RENAL SCINTIGRAPHY ASSESS GLOBAL RENAL FUNCTION RELIABLY?.

E. Durand, A. Prigent. Médecine Nucléaire - CHU Bicétre - Assistance Publique -Hópitaux de Paris.
Le Kremlin Bicétre - France

Technetium-99m-labelled dimercaptosuccinic acid (DMSA) not only has brought improved parenchymal imaging of kidneys, but also has been proposed to quantify both relative and absolute renal function [1].

The latter, however, brings several difficulties: (1) DMSA clearance mechanisms are complex and not always well-correlated to GFR, (2) reliable absolute quantification in scintigraphy is not straightforward, (3) the renal absolute DMSA uptake (ADU) might not truly reflect the absolute renal function, because of changes in plasmatic input function. This work focuses on the last point. As DMSA is cleared from the plasma both by kidneys and other organs, when the function of one kidney decreases, DMSA is cleared more slowly from the blood. The plasmatic input function therefore increases, which should raise the ADU of healthy kidney, even though its function has not changed.

The aim of this study was to prove and quantify this effect. For this, a simple theoretical model (single exponential with clearance rates of 0.27 hr-1 for kidneys and 0.16 hr-1 for other organs; 65% cortical retention, the rest being excreted into urine) was chosen in accordance with the pharmacokinetic data of literature. The ADU of a normal kidney was determined from this model, before and after impairment of the other kidney, assuming that no compensation had occurred. The model showed that this ADU could increase by over 50%, even without any functional change of the healthy kidney. The relative error made when considering that ADU truly measures the absolute renal function was assessed from this model for various levels of kidney dysfunction. The more impaired the kidney and the later the renal scan, the greater the error (always overestimation). Relative renal function however, was not affected with this error. Such an overestimation would not occur either for dynamic tracers for which the very initial plasmatic concentration is quite independent of the renal function.

We conclude that the model fully supports our hypothesis: though DMSA can reliably quantify the relative renal function, it should not be used to assess absolute renal function. in order to avoid gross overestimation of renal function.

[1]- Greshar et al. J Nucl Med 1991: 32, 766-768.