Levels of Fibrinogen Variants Are Altered in Severe COVID-19

Background  Fibrinogen variants as a result of alternative messenger RNA splicing or protein degradation can affect fibrin(ogen) functions. The levels of these variants might be altered during coronavirus disease 2019 (COVID-19), potentially affecting disease severity or the thrombosis risk. Aim  To investigate the levels of fibrinogen variants in plasma of patients with COVID-19. Methods  In this case-control study, we measured levels of functional fibrinogen using the Clauss assay. Enzyme-linked immunosorbent assays were used to measure antigen levels of total, intact (nondegraded Aα chain), extended Aα chain (α _E ), and γ' fibrinogen in healthy controls, patients with pneumococcal infection in the intensive care unit (ICU), ward patients with COVID-19, and ICU patients with COVID-19 (with and without thrombosis, two time points). Results  Healthy controls and ward patients with COVID-19 ( n  = 10) showed similar fibrinogen (variant) levels. ICU patients with COVID-19 who later did ( n  = 19) or did not develop thrombosis ( n  = 18) and ICU patients with pneumococcal infection ( n  = 6) had higher absolute levels of functional, total, intact, and α _E fibrinogen than healthy controls ( n  = 7). The relative α _E fibrinogen levels were higher in ICU patients with COVID-19 than in healthy controls, while relative γ' fibrinogen levels were lower. After diagnosis of thrombosis, only the functional fibrinogen levels were higher in ICU patients with COVID-19 and thrombosis than in those without, while no differences were observed in the other fibrinogen variants. Conclusion  Our results show that severe COVID-19 is associated with increased levels of α _E fibrinogen and decreased relative levels of γ' fibrinogen, which may be a cause or consequence of severe disease, but this is not associated with the development of thrombosis.