Risk Factors and Clinical Outcomes of Hyponatremia in Patients with COVID-19 Admitted to St. Luke's Medical Center-Global City (SLMC-GC) from January 1, 2021, to December 31, 2021: A Case-Control Study

Background: Studies have found that hyponatremia in COVID-19 can result from inflammation-induced non-osmotic release of antidiuretic hormone. This study was conducted to identify the risk factors associated with hyponatremia (Na < 135mmol/L) in COVID-19 patients. The clinical outcomes of COVID-19 patients with and without hyponatremia were also compared. Methods: This case-control study included a total of 384 patients (192 patients each for the hyponatremic and normonatremic groups) aged 18 years old and above diagnosed with COVID-19 infection, who were admitted at SLMC-GC from January 1, 2021 to December 31, 2021. Data pertaining to the patients’ demographic characteristics, comorbid conditions, drug exposure, and laboratory results upon admission were collected and analyzed. The clinical outcomes analyzed include in-hospital mortality, need for ICU admission, need for ventilator support, acute kidney injury, and length of hospital stay. Results: Patients with hyponatremia were found to be significantly older with male predominance. The presence of acute kidney injury had a significant association with hyponatremia. As compared to the normonatremic group, patients with hyponatremia had higher creatinine levels upon admission as well as higher white blood cell count, neutrophil-to-lymphocyte ratio, absolute neutrophil count and inflammatory markers (ferritin, CRP, IL-6, procalcitonin) but lower absolute lymphocyte count. Hyponatremia in COVID-19 patients had also been found to carry about two to three times the risk for adverse outcomes, with a significantly higher proportion of prolonged hospitalization, acute kidney injury, in-hospital mortality, need for ICU admission and need for intubation. Binary logistic regression showed that the significant predictors of hyponatremia include age, presence of acute kidney injury, absolute lymphocyte count, and ferritin level. Conclusion: Hyponatremia in COVID-19 patients is significantly associated with adverse clinical outcomes. Determination of serum sodium is rapid, inexpensive and widely available. It may be used in the local setting to identify COVID-19 patients at high risk for poor clinical outcomes who may benefit from more intensive monitoring and allow proper interventions to be put in place in a timely fashion.