Diagnostic Accuracy of Urinary Creatinine Concentration in the Estimation of Differential Renal Function in Patients with Obstructive Uropathy

Abstract

Objectives: To determine the diagnostic accuracy of spot urine creatinine concentration (UCC) as a new test for the evaluation of differential renal function in obstructed kidneys (DRF_ok) drained by percutaneous nephrostomy tube (PCNT). Methods: In patients with obstructed kidneys drained by PCNT, DRF_ok was derived from UCC by comparing the value of UCC in the obstructed kidney to the value in the contralateral kidney, and was derived from dimercaptosuccinic acid (DMSA) renal scans and creatinine clearance (CCr) using standard methods. Subsequently, the results of UCC were compared to the results of DMSA and CCr. Results: 61 patients were enrolled. Bland-Altman plots to compare DMSA and UCC showed that the upper limit of agreement was 14.8% (95% CI 10.7–18.5) and the lower limit was –19.9% (95% CI –23.8 to –16.1). The sensitivity and specificity of detecting DMSA DRF_ok ≤35% using UCC was 85.2 and 91.2%, respectively. When UCC was compared to CCr, Bland-Altman tests gave an upper limit of agreement of 10.4% (95% CI 7.9–12.8) and a lower limit of agreement of –11.3% (95% CI –13.8 to –8.9). Conclusions: UCC is accurate in the estimation of DRF_ok drained by PCNT.