Renal nephrometry score is associated with urine leak after partial nephrectomy

• To determine if the RENAL nephrometry score is associated with urine leak after partial nephrectomy for tumours ≤ 7 cm.

• Thirty-one patients who developed urine leak after partial nephrectomy between 1998 and 2006 were identified. Each patient was individually matched (1 : 4 by age, gender and surgery date) to 124 patients who had undergone partial nephrectomy but without urine leak. • Associations of RENAL nephrometry scores and each component of the score (Radius; Endophytic; Nearness to collecting system; and Location) with urine leak were evaluated using conditional logistic regression.

• Mean tumour size for the 31 patients who developed urine leak was 3.4 cm (median 3.5; range 1.5-5.9). Mean RENAL score was 8 (median 8; range 5-11). • Each unit increase in RENAL score was associated with a 35% increased odds of urine leak (OR 1.35; 95% CI 1.08-1.69; P= 0.009). • On multivariable analysis, tumours that were <50% exophytic (OR 16.65; 95% CI 2.75-100.71; P= 0.002), completely endophytic (OR 17.02; 95% CI 2.88-100.55; P= 0.002), or located at the renal pole (OR 4.34; 95% CI 1.30-14.53; P= 0.017) were associated with urine leak. • If the score attributed to tumour location was reversed (polar location given a higher score), each unit increase in RENAL score was associated with an 89% increased odds of urine leak (OR 1.89; 95% CI 1.40-2.55; P < 0.001).

• The RENAL nephrometry score is associated with risk of urine leak after partial nephrectomy. When assessing risk of urine leak, reversal of the score attributed to tumour location may improve risk prediction.