Prolonged elevation of D-dimer levels in convalescent COVID-19 patients is independent of the acute phase response

J Thromb Haemost. 2021 Apr;19(4):1064-1070. doi: 10.1111/jth.15267. Epub 2021 Mar 8.


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: One hundred fifty 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 out-patients (n = 81). Clinical examination, chest x-ray, and 6-min walk tests were performed. In addition, a range of coagulation and inflammatory markers were assessed.

Results: Increased D-dimer levels (>500 ng/ml) were observed in 25.3% patients up to 4 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 < .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 (prothrombin time, activated partial thromboplastin time, fibrinogen, platelet count) and inflammation (C-reactive protein, interleukin-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.

Keywords: COVID-19; D-dimer; coagulation parameter; out-patient follow-up.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute-Phase Reaction*
  • Aged
  • COVID-19 / blood*
  • COVID-19 / rehabilitation
  • Female
  • Fibrin Fibrinogen Degradation Products / analysis*
  • Humans
  • Male
  • Middle Aged
  • SARS-CoV-2


  • Fibrin Fibrinogen Degradation Products
  • fibrin fragment D