Etiology and Clinical Features of Patients with Hyponatremia in the Emergency Department: A Cross-Sectional Study

Hyponatremia, a common electrolyte disorder, affects a significant portion of the population, particularly in emergency and hospitalized settings. This study aimed to investigate the causes and clinical characteristics of hyponatremia in emergency department patients. This cross-sectional study included 997 patients diagnosed with hyponatremia in the emergency department between June 2019 and May 2024. We investigated the causes of hyponatremia through medical interviews, blood tests, and urinalysis. We found that for every 1-year increase in age, serum sodium levels in patients with hyponatremia decreased by 0.14 mmol/L, whereas for every 1 mg/dL increase in serum uric acid, the serum sodium levels increased by 0.125 mmol/L. The leading cause of hyponatremia was the syndrome of inappropriate antidiuresis (SIAD), accounting for 357 cases (35.8%). However, a significant number of patients showed a similar diagnostic pattern to that of SIAD but were diagnosed with other conditions, such as cerebral salt wasting (31cases, 5.8%), renal salt wasting (23 cases, 3.8%), and mineralocorticoid-responsive hyponatremia of the elderly (17 cases, 1.8%). Many patients initially diagnosed with SIAD were later found to have one of these alternative conditions upon further evaluation. Fractional excretion values of phosphate and uric acid effectively distinguished SIAD from other conditions. Hyponatremia in the emergency department has diverse causes, with overlapping diagnostic criteria for SIAD and related conditions, though treatment strategies vary significantly. Accurate differential diagnosis is crucial to optimizing patient outcomes. Recognizing the range of underlying causes can help clinicians improve treatment strategies for hyponatremia in emergency settings.