09 November 2020

Scientists believe they have identified the cause of blood clots in some patients with severe COVID-19.

Dr Yogen Kanthi of the US National Heart, Lung, and Blood Institute and colleagues studied blood samples from 172 patients hospitalised with COVID‑19. In more than half of these patients, they identified autoimmune antibodies circulating in the blood which are normally seen in people with the autoimmune disease antiphospholipid syndrome.

These antibodies attack the cells, causing clots in arteries, veins, and capillaries, which may restrict blood flow in the lungs and pose a risk of stroke.

The team explain that this connection between autoantibodies and COVID-19 was unexpected and could prove important. The presence of anti-phospholipid antibodies was also associated with “super-activated” neutrophils which destroy white blood cells.

Dr Kanthi said: “In patients with COVID-19, we continue to see a relentless, self-amplifying cycle of inflammation and clotting in the body. Now we’re learning that autoantibodies could be a culprit in this loop of clotting and inflammation that makes people who were already struggling even sicker.”

Co-author Dr Jason Knight adds: “Half of the patients hospitalised with COVID-19 were positive for at least one of the autoantibodies, which was quite a surprise.

“Antibodies from patients with active COVID-19 infection created a striking amount of clotting in animals - some of the worst clotting we've ever seen. We've discovered a new mechanism by which patients with COVID-19 may develop blood clots."

Details appeared last week in the journal Science Translational Medicine. The team is also carrying out a trial of the anti-clotting agent, dipyridamole, for its ability to reduce excessive blood clots in COVID-19.


Zuo Y, Estes SK, Ali RA, Gandhi AA, Yalavarthi S, Shi H, Sule G, Gockman K, Madison JA, Zuo M, Yadav V, Wang J, Woodard W, Lezak SP, Lugogo NL, Smith SA, Morrissey JH, Kanthi Y, Knight JS. (2020) “Prothrombotic autoantibodies in serum from patients hospitalized with COVID-19.” Science Translational Medicine, doi: 10.1126/scitranslmed.abd3876