Prognostic value of initial serum sodium level in predicting disease severity in patients with COVID-19: A multicenter retrospective study

Introduction: Early prediction of coronavirus disease (COVID-19) severity is crucial. Hyponatremia has been linked to poor outcomes in hospitalized COVID-19 patients, but its association with mild cases is unclear. This study aimed to investigate whether initial serum sodium level is a risk factor for COVID-19 severity in patients with mild -to -moderate disease. Methods: A multicenter retrospective cohort study was conducted in 10 hospitals in Fukui City, Japan, from July 1, 2020, to October 31, 2021. The study included 1055 adult patients with asymptomatic, mild, or moderate COVID-19 confirmed by a positive RT-PCR test. The primary outcome was the need for oxygen therapy after hospitalization, and the secondary outcome was the composite of in -hospital death and critical care interventions. The association between initial serum sodium level (at the emergency department or on admission) and outcomes was examined, adjusting for age, sex, hypertension, and pneumonia presence. Results: Of the 1267 patients diagnosed with COVID-19 during the study period, 1055 were eligible (median age: 45 years; 54 % male). Hyponatremia was observed in 5.2 % of patients upon admission. A lower initial serum sodium level was associated with an increased risk of the need for oxygen therapy after hospitalization (adjusted odds ratio [OR] per 1 mmol/L lower, 1.12 [95 % confidence interval {CI}, 1.05-1.19]) and the composite of critical care and in -hospital death (adjusted OR per 1 mmol/L lower, 1.09 [95 % CI, 0.99-1.20]). Conclusions: Among patients with mild COVID-19, lower initial serum sodium level was a risk factor for COVID19 progression.