Prospectively Estimating the Recoverability of Renal Function after Relief of Unilateral Urinary Obstruction by Measurement of Renal Parenchymal Volume

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Renal parenchymal volume (RPV) has been suggested as an indicator of the potential functional residual capacity for a given kidney. The goal of this study was to determine whether the recoverability of renal function could be predicted by RPV as estimated by computed tomography (CT) before an operation. Eighty-two adult patients diagnosed with long-term chronic unilateral ureteral obstruction and a normal contralateral kidney were recruited for evaluation. RPV was measured by nonenhanced CT. Glomerular filtration rate (GFR) was measured by radioisotope renal scan. Animal models were used to validate use of the CT method to measure RPV. RPV and GFR values for all patients were obtained before surgical relief of the urinary obstruction and compared with those values obtained at 12 months postsurgery. There was no statistically significant difference found between RPV measured by CT or by the water displacement method. Among patient age, sex, and pre-RPV and pre-GFR of obstructed and contralateral kidney, pre-RPV and pre-GFR of obstructed kidney were the independent factors that best indicated recoverability of renal function. Pre-RPV correlated well with post-GFR (r = 0.68, P < .01). The cut-off point of pre-RPV to predict recoverability of renal function after the relief operation was 58.2 mL, as determined by receiver operating characteristic curve analysis. Pre-RPV was the independent factor that determines recoverability of renal function. Renal function may stabilize or improve after relief of urinary obstruction when the pre-RPV value is ≥58.2 mL.