Drain fluid creatinine-to-serum creatinine ratio as an initial test to detect urine leakage following cystectomy: A retrospective study

Introduction: Urine leak following radical cystectomy is a known complication. Among the various methods to diagnose this, assessment of drain fluid creatinine is a relatively easy procedure. We aimed to ascertain the validity of the drain fluid creatinine-to-serum creatinine ratio (DCSCR) as an initial indicator of urinary leak in patients undergoing radical cystectomy. Methods: We retrospectively identified consecutive patients with documentation of drain fluid creatinine in the postoperative period following cystectomy and urinary diversion at our institution between January 2009 and December 2018. All continent diversions and any patient with a DCSCR >1.5:1 underwent contrast study postoperatively. A diagnosis of urine leak was made following confirmatory imaging. Receiver operative characteristic curves were created, and Youden's index was used to determine the strength and clinical utility of DCSCR as a diagnostic test. Results: Two hundred forty-four of the 340 patients included in the study underwent cystectomy with conduit and 81 underwent neobladder creation. Sixteen out of 340 (4.7%) patients had radiologically confirmed urinary leak. DCSCR was elevated in all ureteric anastomotic leaks and in 1 out of the 7 neobladder-urethral anastomotic (NUA) leaks. The sensitivity and specificity of DCSCR to predict all urinary leaks were 68.8% and 80.9% at 1.12 (area under the curve [AUC] = 0.838), whereas at a value of 1.18 (AUC = 0.876) and with the exclusion of NUA leaks, the sensitivity was 77.8% and specificity was 87.6%. Conclusions: DCSCR is a good preliminary test for identifying patients who need prompt confirmatory testing for localizing urinary leaks. A drain creatinine level just 18% higher than the serum creatinine level can signify a urine leak. This is different from general assumptions of a higher DCSCR.