An increase in CD62L(dim) neutrophils precedes the development of pulmonary embolisms in COVID‐19 patients

OBJECTIVES: A high incidence of pulmonary embolism (PE) is reported in patients with critical coronavirus disease 2019 (COVID‐19). Neutrophils may contribute to this through a process referred to as immunothrombosis. The aim of this study was to investigate the occurrence of neutrophil subpopulations in blood preceding the development of COVID‐19 associated PE. METHODS: We studied COVID‐19 patients admitted to the ICU of our tertiary hospital between 19‐03‐2020 and 17‐05‐2020. Point‐of‐care fully automated flow cytometry was performed prior to ICU admission, measuring the neutrophil activation/maturation markers CD10, CD11b, CD16 and CD62L. Neutrophil receptor expression was compared between patients who did or did not develop PE (as diagnosed on CT angiography) during or after their ICU stay. RESULTS: Among 25 eligible ICU patients, 22 subjects were included for analysis, of whom nine developed PE. The median (IQR) time between neutrophil phenotyping and PE occurrence was 9 (7‐12) days. A significant increase in the immune‐suppressive neutrophil phenotype CD16(bright)/CD62L(dim) was observed on the day of ICU admission (P = 0.014) in patients developing PE compared to patients who did not. CONCLUSION: The increase in this neutrophil phenotype indicates that the increased number of CD16(bright)/CD62L(dim) neutrophils might be used as prognostic marker to predict those patients that will develop PE in critical COVID‐19 patients.