Nucleated red blood cells as a prognostic marker for mortality in patients with SARS-CoV-2-induced ARDS: an observational study.

Background: The presence of nucleated red blood cells (NRBCs) in the peripheral blood of critically ill patients is associated with poor outcome. Evidence regarding the predictive value of NRBCs in patients with SARS-CoV-2-induced acute respiratory distress syndrome (ARDS) remains elusive. The aim of this study was to evaluate the predictive validity of NRBCs in these patients.

Methods: Daily NRBC values of adult patients with SARS-CoV-2-induced ARDS were assessed and their predictive validity for mortality was statistically evaluated. A cut-off level based on the patient's maximum NRBC value during ICU stay was calculated and further specified according to Youden's method. Based on this cut-off value, further analyses such as logistic regression models and survival were performed.

Results: 413 critically ill patients with SARS-CoV-2-induced ARDS were analyzed. Patients who did not survive had significantly higher NRBC values during their ICU stay compared to patients who survived (1090/µl [310; 3883] vs. 140/µl [20; 500]; p < 0.0001). Patients with severe ARDS (n = 374) had significantly higher NRBC values during ICU stay compared to patients with moderate ARDS (n = 38) (490/µl [120; 1890] vs. 30/µl [10; 476]; p < 0.0001). A cut-off level of NRBC ≥ 500/µl was found to best stratify risk and was associated with a longer duration of ICU stay (12 [8; 18] vs. 18 [13; 27] days; p < 0.0001) and longer duration of mechanical ventilation (10 [6; 16] vs. 17 [12; 26] days; p < 0.0001). Logistic regression analysis with multivariate adjustment showed NRBCs ≥ 500/µl to be an independent risk factor of mortality (odds ratio (OR) 4.72; 95% confidence interval (CI) 2.95-7.62, p < 0.0001). Patients with NRBC values below the threshold of 500/µl had a significant survival advantage over those above the threshold (median survival 32 [95% CI 8.7-43.3] vs. 21 days [95% CI 18.2-23.8], log-rank test, p < 0.05). Patients who once reached the NRBC threshold of ≥ 500/µl during their ICU stay had a significantly increased long-term mortality (median survival 489 days, log-rank test, p = 0.0029, hazard ratio (HR) 3.2, 95% CI 1.2-8.5).

Conclusions: NRBCs predict mortality in critically ill patients with SARS-CoV-2-induced ARDS with high prognostic power. Further studies are required to confirm the clinical impact of NRBCs to eventually enhance decision making.