PE-149 : Diagnostic Usefulness of the Spot Urine Sodium/Potassium Ratio in Cirrhotic Patients with Ascites

Aims: A low-salt diet is considered important for the control of ascites in cirrhotic patients. The 24-hour (24-h) urine sodium (Na) excretion test is a standard method performed to determine low-salt diet compliance. Considering that measuring 24-h urine Na excretion is a time-consuming method, the spot urine Na/potassium (K) ratio can be alternatively measured. However, whether 24-h urine Na excretion can be alternatively replaced with the spot urine Na/K ratio has not been fully validated yet. Hence, this study aimed to validate whether the spot urine Na/K ratio could replace 24-h urine Na excretion in assessing low-salt diet compliance. Methods: A total of 192 patients with liver cirrhosis and ascites were screened. We prospectively studied 175 patients who met the inclusion criteria. Furthermore, 24-h urine collection was performed, and 5-mL spot urine was collected in the morning. Subsequently, 24-h urine Na, creatinine (Cr) level, and spot urine Na and K were assessed. A complete urine collection was confirmed based on 24-h Cr excretion levels of 15 mg/kg/day for men and 10 mg/kg/day for women. The area under the receiver operating characteristic (AUROC) curve analysis was performed to evaluate the feasibility of the spot urine Na/K ratio in predicting 24-h urine Na greater than 78 mmol/day. Results: Out of the 175 patients, 24-h urine samples were completely collected in 57 patients only. Moreover, urine samples were not completely collected in 118 patients because their 24-h urine Cr excretion level was less than the established criteria. There was no significant difference in age, sex, etiology of liver cirrhosis, Child-Pugh class, and Model for End-Stage Liver Disease score between the two groups. In the complete urine collection group, the AUROC curve for the spot urine Na/K ratio in predicting 24-h urine Na greater than 78 mmol/day was 0.874 ± 0.051 (P<0.001). In the incomplete urine collection group, the AUROC was 0.832 ± 0.039 (P<0.001). Both groups showed similar AUROC values. In the complete urine collection group, the classical cutoff value greater than 1.0 of the spot urine Na/K ratio showed 90.9% sensitivity, 56.0% specificity, 73.2% positive predictive value (PPV), and 82.4% negative predictive value (NPV). The best cutoff value for the spot urine Na/ K ratio was 1.5, with 87.9% sensitivity and 80.0% specificity. In all patients, the AUROC was 0.841 ± 0.031 (P<0.001), with 94.1% sensitivity, 47.9% specificity, 71.6% PPV, and 85.4% NPV when the cutoff value of the spot urine Na/K ratio was 1.0. Among the studied patients, 131 collected their urine during hospitalization. Complete urine collection did not differ between the inpatient group (34.4%) and the outpatient group (29.5%) (P=0.348). Conclusions: The spot urine Na/K ratio reflects 24-h urine Na, but the AUROC value obtained in this study is lower than that of a previous study. However, drawing conclusions based on the results of the study is difficult considering the large number of patients with incomplete urine collection. Even in hospitalized patients, several incomplete urine collections are observed, making it difficult to accurately check 24-h urine Na. Therefore, a method that more easily identifies low-salt diet compliance in cirrhotic patients with ascites is required in the future.