MPO and COVID-19: For all 3 markers, we observed that all COVID-19 patients (n = 96) have significantly more NETs than healthy donors (n = 10), respectively: total cell-free DNA concentrations [304 ng/ml (209–443) vs. 140 ng/ml (124–151), p < 0.0001], plasma MPO–DNA levels [0.63ST (0.15–3.10) vs. 0.044 ST (0.012–0.093), p < 0.0001], and plasma H3Cit levels [0.37 (0.16–1.06) vs. 0.14 (0.088–0.18), p < 0.01].