Early neutrophil responses are potential biomarkers to predict severe COVID-19 in adults

In the early COVID-19 pandemic, the strain on healthcare facilities highlighted the need for reliable biomarkers to predict progression to severe COVID-19. Neutrophils, the most abundant leukocytes in circulation, are early defenders against pathogens. In a Singaporean adult cohort, early neutrophil mediators were assessed for their suitability as prognostic biomarkers of COVID-19 complications. Plasma levels of myeloperoxidase (MPO), elastase, soluble urokinase plasminogen activator receptor (suPAR), and soluble suppressor of tumorigenicity 2 (sST2) in 35 nonsevere and 14 severe cases were measured twice, 2 to 7 d apart after hospitalization. Nineteen controls were included. The levels of MPO, elastase, suPAR, and sST2 were significantly higher in patients with severe COVID-19 compared with those with mild and healthy controls. At baseline sampling, MPO and suPAR predicted severe COVID-19 and had AUROCs of 0.76 and 0.87, respectively. MPO and suPAR at cut-off values of 26.41 ng/mL and 3.19 ng/mL, respectively showed approximately 71% sensitivity and 81% to 84% specificity to differentiate severe COVID-19. In contrast, elastase and neutrophil counts were less predictive of severe disease. In adult COVID-19, MPO and suPAR may be reliable prognostic biomarkers of severe disease during acute COVID-19. Further validation of these markers in a larger cohort and in other infectious diseases is warranted.