Variation of the Neutrophil-to-Lymphocyte Ratio and Mean Platelet Volume in a Multicenter Study of Critically Ill Patients with COVID-19 Living at Different Altitudes

Background: Evidence on the prognostic utility of biological markers in critically ill patients with COVID-19 across different geographic altitudes remains limited. Objectives: The aim of this study was to determine the prognostic value of inflammatory and hematological markers, particularly the neutrophil-to-lymphocyte ratio (NLR) and mean platelet volume (MPV), for mortality risk in critically ill patients with COVID-19 receiving invasive mechanical ventilation and living at different geographic altitudes. Methods: A multicenter retrospective cohort study was conducted using secondary data from a clinical database. A total of 362 critically ill patients with COVID-19 admitted to intensive care units (ICUs) between April 2020 and March 2022 were included. Patients were treated at three hospitals in Ecuador located at different altitudes: sea level (4 m above sea level [masl]), moderate altitude (2200 masl), and high altitude (2850 masl). Clinical, laboratory, and outcome data were obtained from electronic medical records. Results: The mean age was 54.44 years, and 71.27% of patients were male. Post hoc, altitude-stratified NLR and MPV thresholds were associated with increased odds of ICU mortality: at sea level, NLR ≥ 12.50 and MPV ≥ 8.80 fL; at moderate altitude, NLR ≥ 11.50 and MPV ≥ 9.80 fL; and at high altitude, NLR ≥ 16.30 and MPV ≥ 9.00 fL. Conclusions: In mechanically ventilated patients with critical COVID-19, NLR and MPV values above post hoc, altitude-stratified cutoff points were associated with higher ICU mortality. However, because each altitude stratum corresponded to a different hospital and these thresholds were not ROC-derived or internally/externally validated, these findings should be interpreted as exploratory and hypothesis-generating.