Neutrophil calprotectin identifies severe pulmonary disease in COVID-19

Severe cases of coronavirus disease 2019 (COVID-19) are regularly complicated by respiratory failure. While it has been suggested that elevated levels of blood neutrophils associate with worsening oxygenation in COVID-19, it is unknown whether neutrophils are drivers of the thrombo-inflammatory storm or simple bystanders. We now report that patients with COVID-19 (n=172) have markedly elevated levels of the neutrophil activation marker S100A8/A9 (calprotectin) in their blood. Calprotectin tracked with other acute phase reactants including C-reactive protein, D-dimer, ferritin, and absolute neutrophil count, but was superior in identifying patients requiring mechanical ventilation. In longitudinal samples, calprotectin rose as oxygenation worsened. When tested on day 1 or 2 of hospitalization (n=94 patients), calprotectin levels were significantly higher in patients who progressed to severe COVID-19 requiring mechanical ventilation (8039 +/- 7031, n=32) as compared to those who remained free of intubation (3365 +/- 3146, p