The prognostic importance of residual kidney function (RKF) for maintenance hemodialysis (HD) patients has previously been recognized.1-6 In previous studies, monitoring of RKF typically required urine collection preceding the HD session and a predialysis blood sample from the end of collection to compute the renal clearance of urea/creatinine (ie, urinary urea/creatinine divided by serum concentration2,4,5) and more specifically, renal Kt/Vurea.3 Urine volume, the prerequisite for RKF, can also be estimated by patient self-report.