Complaints of lower urinary tract symptoms (LUTS) increase with age. Among LUTS cases, overactive bladder (OAB), characterized by urinary urgency as the primary symptom occasionally accompanied by nocturia and urinary incontinence, significantly affects patient quality of life (QOL). While OAB is associated with multiple factors, lifestyle-related illnesses such as hypertension and diabetes mellitus are of particular interest among these. These lifestyle-related illnesses are often caused by improper diet, lack of exercise, and other daily activities, which are also common factors leading to the onset of OAB. Given this background, in actual clinical practice, behavioral therapies such as diet and exercise are recommended as the most preferred treatment for OAB and lifestyle-related illnesses.
Regarding dietary therapy, the importance of balanced sodium (Na) and potassium (K) intake is particularly emphasized in treating hypertension. The urinary Na/K ratio has recently been shown to be an important predictor of the development of hypertension, especially as it reflects the balance of these intakes. A diet that improves the urinary Na/K ratio is also believed to be effective in treating hypertension and, consequently, reducing oxidative stress. However, the usefulness of the urinary Na/K ratio as a diagnostic and predictive factor for treating OAB, for which salt restriction and promotion of vegetable intake are potential dietary options, as in hypertension, has not yet been studied.
Therefore, the purpose of the present study was to evaluate the usefulness of the urinary Na/K ratio as a diagnostic predictor of OAB. Specifically, this study compared the urinary Na/K ratios of OAB and non-OAB patient groups to determine how the urinary Na/K ratio affects the prevalence of OAB symptoms. This study also clarified the relationship between the urinary Na/K ratio and each symptom of OAB and QOL.

We conducted a cross-sectional, multicenter study of women aged 20 years or older with newly diagnosed OAB between January and December 2023. We also used female non-OAB volunteers who participated during the same period as controls.
The Overactive Bladder Symptom Score (OABSS) was used to diagnose OAB, and OAB was defined as a score of 2 or more on OABSS question 3 (urinary urgency) and a total score of 3 or more. Urinary Na/K was calculated using the spot urine sample. After clarifying the relationship between the presence of OAB and urinary Na/K, we examined in detail the extent of LUTS, including OAB, at different urinary Na/K levels based on cutoff values obtained from receiver operating characteristic (ROC) curves.
Subjective symptoms related to LUTS were evaluated using OABSS and International Prostate Symptom Score (IPSS), and uroflowmetry and post-void residual urine volume using ultrasound sonography were used to evaluate objective findings. P<0.05 was considered a statistically significant difference.

There were 85 eligible participants (35 in the OAB group, 41.2%). The mean age was 65.4±14.7 years, with the OAB group older (non-OAB group, 62.3±15.9 years; OAB group, 69.8±11.6 years; P=0.028). Urinary Na/K was higher in the OAB group (non-OAB, 3.65±2.28; OAB, 4.60±2.79; P=0.043). The cutoff value of urinary Na/K for OAB incidence calculated using the ROC curve was 3.96 [sensitivity 0.715, specificity 0.702, area under the curve (AUC) 0.733, P=0.012].
When the two groups were divided by urinary Na/K levels based on ROC cutoffs, the high urinary Na/K (H) group had significantly higher OABSS Q3 (urinary urgency) and Q4 (urgency incontinence) and total scores than the low (L) group [(Q3; L group, 1.2±1.6; H group, 2.0±1.8; P=0.045), (Q4; L group, 0.8±1.3; H group, 1.6±1.8; P=0.030), (total score; L group, 4.2±3.8; H group, 6.0±4.0; P=0.040)]. Regarding IPSS, Q1 (Incomplete Emptying) and Q4 (urinary urgency) were higher in the H group (Q1; L group, 0.6±1.1; H group, 1.1±1.4; P=0.028) and (Q4; L group, 0.8±1.3; H group, 1.8±1.9; P=0.008).
Regarding other findings, the H group had a lower voided volume (L group, 217.8±73.2 mL; H group, 175.9±80.2 mL; P=0.022) and a significantly lower maximum flow rate (L group, 20.1±6.1 mL/s; H group, 16.8±6.3 mL/s; P=0.036). Further, when urinary Na/K was included in addition to age, hypertension, type II diabetes, and other factors known to contribute to OAB, high urinary Na/K (>3.96) was an independent risk factor for OAB in univariate analysis and in multivariate analysis (odds ratio, 7.32; 95% confidence interval, 2.15–29.16; P=0.011). After adjusting for these risk factors for OAB, urinary Na/K was still a risk factor for OAB using propensity score matching (P=0.003).

According to the results of this study, there is a significant association between urinary Na/K and the prevalence and severity of OAB. Notably, in the H group, the main symptoms of OAB, such as urinary urgency and urgent urinary incontinence, and the IPSS indicated a strong sense of incomplete bladder emptying. In objective findings, group H patients also showed decreased voided volume and decreased maximal urinary flow rate. Various statistical analyses also revealed that the urinary Na/K ratio is an independent risk factor for OAB.

Elevated urinary Na/K is an independent risk factor for OAB and may be a convenient predictor for diagnosis and prevention.

Continence 12S (2024) 101563
DOI: 10.1016/j.cont.2024.101563