Background: Persistent fatigue, breathlessness and reduced exercise tolerance have been reported following acute COVID-19 infection. Although immuno-thrombosis has been implicated in acute COVID-19 pathogenesis, the biological mechanisms underpinning Long COVID remain unknown. We hypothesized that pulmonary microvascular immuno-thrombosis may be important in this context.
Methods: 150 COVID-19 patients were reviewed at St James's Hospital Dublin between May and September 2020 at a median of 80.5 (range 44 - 155) days after initial diagnosis. These included patients hospitalized during initial illness (n=69) and others managed entirely as outpatients (n=81). Clinical examination, chest x-ray and 6-minute walk tests were performed. In addition, a range of coagulation and inflammatory markers were assessed.
Results: Increased D-dimer levels (>500ng/ml) were observed in 25.3% patients up to four months post-SARS-CoV-2 infection. On univariate analysis, elevated convalescent D-dimers were more common in COVID-19 patients who had required hospital admission and in patients aged more than 50 years (p<0.001). Interestingly, we observed that 29% (n=11) of patients with elevated convalescent D-dimers had been managed exclusively as out-patients during their illness. In contrast, other coagulation (PT, APTT, fibrinogen, platelet count) and inflammation (CRP, IL-6 and sCD25) markers had returned to normal in > 90% of convalescent patients.
Conclusions: Elucidating the biological mechanisms responsible for sustained D-dimer increases may be of relevance in Long COVID pathogenesis and has implications for clinical management of these patients.
