BACKGROUND & AIMS: Estimates of glomerular filtration rate (GFR) are used to assess renal function and are an independent prognostic factor for patients with decompensated cirrhosis, but are impractical for routine use. We investigated whether the ratio of sodium to potassium in randomly collected urine samples (UNa/K) is associated with mortality and renal dysfunction in patients with decompensated cirrhosis and ascites.METHODS: We assessed data from 126 consecutive patients with decompensated cirrhosis and ascites (93 men; age, 56 ± 12 y; 55% with viral-related disease) admitted to the Hippokration General Hospital of Thessaloniki, Greece, from September 2010 through January 2012. At admission, clinical and laboratory variables were recorded, including GFR, measured with (51)Cr-EDTA. Urine samples were collected, and UNa/K was determined. We evaluated the association between UNa/K and patient mortality using the area under the receiver operating characteristic curve analysis.RESULTS: Forty-one patients (32%; group 1) had a GFR less than 60 mL/min, and 85 patients (68%; group 2) had a GFR of 60 mL/min or greater. In the multivariable analysis, 3 variables were associated independently with the presence of severe renal dysfunction (GFR, <60 mL/min): age (odds ratio [OR], 0.93; P = .008), systolic blood pressure (OR, 1.05; P = .022), and UNa/K (OR, 1.5; P = .025). A UNa/K less than 1.0 had high sensitivity and a negative predictive value for the presence of GFR less than 60 mL/min (79% and 87%, respectively) and mortality (68% and 91%, respectively).CONCLUSIONS: In patients with decompensated cirrhosis and ascites, a ratio of sodium to potassium of less than 1 in randomly collected urine samples was associated with renal dysfunction and short-term mortality. These findings require confirmation in additional studies.