On 19th October, Wiley online published an article entitled ‘No evidence of hypercoagulability, altered fibrinolysis, or increased fibrin(ogen) microaggregates in never-hospitalized Long Covid‘ (Fraser et al, 2026), which discusses the microclot theory and potential use of anticoagulant medicaton for Long Covid.
Summary (from the article)
In summary, in never-hospitalized patients with specialist-confirmed Lond Covid (LC), we found no evidence of persistent prothrombotic activation, impaired fibrinolysis, abnormal fibrin fiber architecture or increased fibrin(ogen) microaggregates, and no meaningful associations with breathlessness, fatigue or pulmonary perfusion and gas transfer metrics.
These findings suggest that antithrombotic therapy is not justified outside of clinical trials for never-hospitalized LC or in the absence of a separate recognized indication such as venous or arterial thrombosis.
MEA Comment
This is an important new research study from Oxford which casts further doubt on the idea that small blood clots – microclots – are involved in the causation of Long Covid
In addition, these results do not support the use of anticoagulant (‘blood thinning') drugs for treating Long Covid
Dr Charles Shepherd,
Trustee and Hon. Medical Adviser to the ME Association,
Member of the 2018-2021 NICE guideline on ME/CFS committee,
Member of the 2002 Chief Medical Officer's Working Group on ME/CFS
More Information:
- Medical Matters: Are the researchers any further forward in deciding whether microclots play a role in the causation of Long Covid, and possibly ME/CFS? And is there any evidence that blood-thinning drugs, or blood-exchange procedures such as apheresis, are effective forms of treatment for either condition? | Autumn 2026
- Medical Matters: Has there been any progress with the research that has been looking at the presence of ‘micro-clots’ in Long Covid and possibly in ME/CFS as well? | Spring 2024