PURPOSE: To determine prevalences of common geriatric syndromes in the setting of different normal ranges of serum sodium. METHODS: In this cross-sectional study, 2048 older adults (aged ≥ 60) who underwent comprehesive geriatric assessment between 2016 and 2023 in one geriatric outpatient clinic were evaluated. Patient groups included moderate hyponatremia (<
130 mEq/L, n = 28, 1.6%), mild hyponatremia (130-134 mEq/L, n = 130, 7.3%), lower-normal range (135-140 mEq/L, n = 904, 50.4%), upper normal range (141-145 mEq/L, n = 702, 39.2%), and hypernatremia (>
145 mEq/L, n = 29, 1.6%). A separate analysis was also performed according to the following classification: borderline hyponatremia (133-137 mEq/L), normal (138-142 mEq/L), and borderline hypernatremia (143-147 mEq/L). Logistic regression analysis was performed to determine associations between serum sodium groups and geriatric syndromes. RESULTS: After applying the inclusion/ exclusion criteria a total of 1792 patients were included, with a mean age of 81 ± 8 years and 71% were female. With the exception of geriatric depression, all other syndromes were more prevalent in the lower-normal range than the upper normal range. After adjustments for age, sex, comorbidities, functional status, and drug exposures, upper normal range of serum sodium was associated with lower risks of dependency (OR 0.72, 95% CI 0.53-0.99, p = 0.043) and malnutrition (OR 0.69, 95% CI 0.51-0.94, p = 0.018). Compared to borderline hyponatremia, borderline hypernatremia was associated with lower risks of polypharmacy (OR 0.58, 95% CI 0.37-0.89, p = 0.014), dependency based on basic activities of daily living (OR 0.55, 95% CI 0.31-0.98, p = 0.042), malnutrition (OR 0.55 95% CI 0.33-0.91, p = 0.020), and frailty (OR 0.65, 95% CI 0.44-0.96, p = 0.031). CONCLUSIONS: Compared to a lower normal level of sodium, an upper normal level of sodium was associated with a lower risks of dependency and malnutrition. Borderline hypernatremia was associated with lower prevalences of polypharmacy, dependency, frailty, and malnutrition compared to borderline hyponatremia among geriatric outpatients in this single-center study.