Hyponatremia after COVID-19 is frequent in the first year and increases re-admissions.

Hyponatremia on admission has been related to worse outcomes in patients with COVID-19 infection. However, little is known about the frequency and the associated risk factors of hyponatremia after COVID-19 discharge. We performed an observational 24-month follow-up study of patients admitted during the first COVID-19 wave. Kaplan-Meier curves and Cox proportional hazard models were used to assess the main variables in predicting hyponatremia on follow-up (HYPO-FU). A total of 161 out of 683 (24.4%) developed HYPO-FU. The group with HYPO-FU comprised of more men [(62.3%) vs. (49.2%); p < 0.01], older [65.6 ± 18.2 vs. 60.3 ± 17.0; p < 0.01] and more frequently re-admitted [(16.2%) vs. (3.8%); p < 0.01). The rate of HYPO-FU was higher in the first year 23.6 per 100 individuals per year. After Cox regression analysis, the independent risk factors of HYPO-FU were diabetes [OR 2.12, IC 95% (1.48-3.04)], hypertension [OR 2.18, IC 95% (1.53-3.12)], heart failure [OR 3.34, IC 95% (1.72-6.48)] and invasive ventilation support requirement [OR: 2.38, IC 95% (1.63-3.50)]. To conclude, HYPO-FU was frequent in the first year after COVID-19 infection, and the risk was higher in older men with comorbidities, increasing rehospitalisation. Further studies aimed at evaluating the beneficial effects of correcting hyponatremia in these patients are warranted.