Assessment of drainage in PUJ dilatation: pelvic excretion efficiency as an index of renal function.

Renal function is important when assessing the response of a dilated renal pelvis to a diuretic stimulus. Yet there is little in the literature to suggest how this should be undertaken. Our aim was to develop a model which we have called pelvic excretion efficiency (PEE). The PEE, which may be used to assess drainage, is a mathematical model of the ratio of the total kidney excretion to the total amount of isotope extracted from the blood by the kidney. Thirty-three children with a prenatal diagnosis of unilateral renal pelvic dilatation (PUJ) were treated conservatively after birth. As a group, they underwent a total of 164 diuretic DTPA renograms up to the age of 72 months. Drainage was assessed as the response to frusemide (defined as the time for the corrected renal curve to fall to 75% of the maximum value in the frusemide part of the study; T75), response to bladder emptying, a change of posture after frusemide (PM), and PEE. The contralateral normal kidney showed a combination of both 'good' T75 and PM drainage in 51% of renograms while the PEE showed drainage in all. The affected kidney with renal pelvic dilatation showed a combination of both 'poor' T75 and PM drainage in 42% of renograms. The PEE was low in 99% of these 'poor drainage' renograms. The PEE, the ratio of the mathematical model of renal uptake to excretion, is readily calculated and may be a more accurate and specific technique to assess drainage on diuretic renography.