In the serum from patients hospitalized with COVID-19, levels of NET markers did not correlate with disease severity or D-dimer levels but did correlate with lower anti-RBD antibody titers. (A) Serum levels of MPO-DNA from patients hospitalized with COVID-19 and control patients, normalized to NET-standard. (B) Scatter plot of D-dimer vs MPO-DNA levels in patient serum showing no correlation between the two (R² = 0.0217, P = .29 from linear regression analysis). Dotted horizontal lines indicate low (<0.5 μg/mL fibrinogen equivalent units, or FEU), mid (between 0.5 and 2 μg/mL FEU), and high (>2 μg/mL FEU) D-dimer levels. Dotted vertical lines indicate low (<0.33), mid (0.33-0.5), and high (>0.5) levels of MPO-DNA. Dot colors indicate patients with low (red), mid (orange), or high (green) anti-RBD titers. (C) Scatter plot of anti-RBD antibody titers vs MPO-DNA levels in patient serum (R² = 0.1487, P = .0043 from linear regression analysis). Dotted horizontal lines indicate low (<4), mid (4.5-5.5), and high (>6) anti-RBD antibody titers, and dotted vertical lines are as in panel B. Dot colors indicate patients with high (red), mid (orange), or low (green) levels of D-dimer. (D) Average MPO-DNA levels from patients with low (2-4), mid (4.5-5.5), or high (6-8) titers of anti-RBD antibodies. (E) Proportion of patients in each anti-RBD titer group (low, mid, or high) who had low, mid, or high MPO-DNA levels. (F) Average anti-RBD titers from patients with low (<0.33), mid (0.33-0.5), or high (>0.5) MPO-DNA levels. (G) Proportion of patients in each MPO-DNA group (low, mid, or high) who had low, mid, or high anti-RBD titers. In panels A, D, and F, dashed line represents the median for each group and dotted lines represent the first and third quartiles. In panel A, ∗∗P < .01 by unpaired two-tailed t test and in panels D and F, ∗P < .05, ∗∗P < .01 by one-way ANOVA test with Tukey multiple comparisons test.