508. Biomarker elevation during COVID-19: Differences between ambulatory and hospitalized individuals

Background: While the majority of illness due to COVID-19 does not require hospitalization, little has been described about the host inflammatory response in the ambulatory setting Differences in the levels of inflammatory signaling proteins between outpatient and hospitalized populations could identify key maladaptive immune responses during COVID-19 Methods: Samples were collected from 76 participants (41% female, mean 46 8 years of age) enrolled at five military treatment facilities between March 20, 2020 and June 17, 2020 in an ongoing prospective COVID-19 cohort This analysis was restricted to those with positive SARS-CoV-2 (severe acute respiratory syndrome- coronavirus 2) RT-PCR testing and included hospitalized (N=29;10 requiring an ICU stay) and non-hospitalized (N=43) participants Severity markers (IL6, D-dimer, procalcitonin, ferritin, ICAM-1, IL5, lipocalin, RAGE, TNFR, VEGFA, IFNγ, IL1β) were measured in plasma (mg/dL) using the Ella immunoassay and natural log transformed Univariate negative binomial regression was performed to determine relative risk of hospitalization Using the full marker panel, we performed a Principal Component Analysis (PCA) to determine directions of maximal variance in the data Pearson's correlation coefficient was determined between analytes and each axis Results: Participants requiring ambulatory-, hospital-, and ICU-level care had samples collected at 44 0 (IQR: 35 0-51 0), 40 0 (13 0-51 0), and 47 5 (21 0-54 0) days, respectively Higher unadjusted levels of IL6, D-dimer, procalcitonin, or ferritin were each associated with hospitalization (Table 1) The PCA showed a separation along axes between level of care and duration of symptoms (Fig 1) While significant correlations were noted with a number of biomarkers, PC1 most correlated with TNFR1 (r=0 88) and PC2 most correlated with IL6Ra (r=0 95) PC1 axis variation accounted for 36 5% of variance and the PC2 axis accounted for 20 0% of variance Conclusion: TNFR1 and IL6Ra levels correlated with differences in the proinflammatory states between hospitalized and non-hospitalized individuals including time points late in the course of illness Further analysis of these preliminary findings is needed to evaluate for differences by stages of illness