Abstract
Excess neutrophilic inflammation is associated with poor prognosis in a number of acute and chronic respiratory infections [1]. Increased numbers of circulating neutrophils are observed during acute respiratory tract infections including COVID-19, where in particular increased numbers of immature neutrophils are associated with more severe disease [2]. S100A8/A9 (calprotectin) is an antimicrobial complex found in the cytoplasm and granule membranes of neutrophils, and is released by activated neutrophils during neutrophil extracellular trap (NET)osis [3]. Serum S100A8/A9 levels are increased in sepsis [4] and COVID-19 [5–7], as well as other acute [8] and chronic lung diseases [9, 10], and correlate with disease severity [11].
A rapid, quantitative serum S100A8/A9 (calprotectin) lateral flow test in combination with clinical status predicted outcomes in people hospitalised with COVID-19 and associated with a patient cluster driven by markers of neutrophil activation
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