High quality analysis of circulating biomarkers reveals no evidence of elevated inflammatory markers in a long COVID cohort recruited at a primary care center

Long COVID (LC) is a broad label encompassing the heterogeneous long-term consequences of SARS-CoV-2 infection that persist for at least 2–3 months post-infection. Despite its substantial global burden, there is still a lack of reliable biomarkers or panels capable of distinguishing individuals with Long COVID from healthy individuals or from those who have recovered from acute COVID-19. We previously characterized a biomarker panel comparing 85 adults with WHO-defined Long COVID against 85 age- and sex-matched controls who had recovered within three months of acute COVID-19 in 2020, at 12–24 months post-infection. That initial profile evaluated blood cell counts, coagulation status, routine SARS-CoV-2 serology, immune cell populations, and basic cytokine levels based on Luminex assays. We have enhanced our biomarker panel by incorporating more precise cytokine quantification using the high-precision ELLA automated immunoassay system. To assess potential ongoing peripheral systemic inflammation, we measured classical inflammatory markers in blood, including C-reactive protein (CRP), tumor necrosis factor alpha (TNFα), interleukin (IL)-1β, and IL-6. In this manuscript, we present data that confirm age- and gender-matching between the LC and control group; and compared differences in cytokine levels and comorbidities.