Background Dysnatremia is an independent predictor of mortality in patients with bacterial pneumonia. There is paucity of data about the incidence and prognostic impact of abnormal sodium concentration in patients with coronavirus disease 19 (COVID-19). Methods This retrospective longitudinal cohort study, including all adult patients who presented with COVID-19 to two hospitals in London over an 8-week period, evaluated the association of dysnatremia (serum sodium < 135 or > 145 mmol/L, hyponatremia and hypernatremia, respectively) at several timepoints with inpatient mortality, need for advanced ventilatory support and acute kidney injury (AKI). Results The study included 488 patients (median age 68 years). At presentation, 24.6% of patients were hyponatremic, mainly due to hypovolemia, and 5.3% hypernatremic. Hypernatremia two days after admission and exposure to hypernatremia at any timepoint during hospitalization were associated with a 2.34-fold (95% CI 1.08 – 5.05, p=0.0014) and 3.05-fold (95% CI 1.69 – 5.49, p<0.0001), respectively, increased risk of death compared to normonatremia. Hyponatremia at admission was linked with a 2.18-fold increase in the likelihood of needing ventilatory support (95% CI 1.34-3.45, p= 0.0011). Hyponatremia was not a risk factor for in-hospital mortality, except for the subgroup of hypovolemic hyponatremia. Sodium values were not associated with the risk for AKI and length of hospital stay. Conclusion Abnormal sodium levels during hospitalization are risk factors for poor prognosis, with hypernatremia and hyponatremia being associated with a greater risk of death and respiratory failure, respectively. Serum sodium values could be used for risk stratification in patients with COVID-19.

This study showed that hyponatraemia is an independent predictor of mortality, and hyponatraemia per se is likely to contribute to excess mortality. Further studies are needed to examine whether correction of hyponatraemia can reduce mortality.

Tolvaptan is effective in correcting hyponatraemia. Without rigorous electrolyte monitoring, tolvaptan carries a significant risk of overly rapid sodium correction, especially in patients with starting sNa <125 mmol/l. Tolvaptan should be used with great caution under close electrolyte monitoring.