Serum osmolarity as a predictor of mortality in ICU COVID-19 patients: a retrospective analysis

Background Serum osmolarity, reflecting fluid and electrolyte balance, may serve as a prognostic marker in critically ill patients, but its role in COVID-19 is not well established. This study evaluated the association between admission serum osmolarity and in-hospital mortality in critically ill COVID-19 patients. Methods We conducted a retrospective study including 267 critically ill COVID-19 patients admitted from the ED to the ICU of a tertiary-care hospital between March 2020 and April 2022. Data on demographics, thoracic computed tomography (CT) findings, vasopressor use, ventilation support, laboratory values, and in-hospital mortality were obtained. Serum osmolarity was calculated using the formula. The primary outcome was in-hospital mortality; secondary outcomes included vasopressor use, endotracheal intubation (ETI), and laboratory parameters. Statistical analyses included Mann–Whitney U and chi-square tests, logistic regression, and receiver operating characteristic (ROC) curve analysis. Results Of 267 patients, 203 were non-survivors and 64 survivors (mortality 76%); mean age was 53.8 ± 12.3 years, 59.6% male. Survivors had higher median serum osmolarity (288.37 vs. 285.75 mOsm/L, p = 0.034) and sodium (Na) (135 vs. 133 mEq/L, p = 0.004). Sodium demonstrated slightly superior discrimination (AUC = 0.620) compared to osmolarity (area under the curve (AUC) = 0.588). In multivariate logistic regression, serum sodium (OR = 0.89, 95% CI 0.82–0.97), inotropic agent use (OR = 3.73, 95% CI 1.65–8.42), and endotracheal intubation (OR = 5.20, 95% CI 2.11–12.84) were independent predictors of mortality. The model’s c-statistic was 0.713 (95% CI 0.654–0.771) with 70.4% sensitivity and 65.8% specificity. Conclusions Lower admission serum osmolarity and hyponatremia were independently associated with increased in-hospital mortality in critically ill COVID-19 patients. Although Na slightly outperformed calculated osmolarity, the latter remains a practical, integrative prognostic tool for early risk stratification. Prospective studies should evaluate whether timely correction of hypo-osmolar or hyponatremic states improves outcomes.