Menu

‘Long COVID’ May Be Caused By Abnormal Blood Clotting

Still unknown are biological mechanisms of symptoms long after initial infection

Some COVID-19 patients report experiencing symptoms including fatigue, muscle pain, brain fog and headaches long after the infection has cleared up — so-called Long COVID — and now researchers in Ireland say abnormal blood clotting may be the key.

Even once inflammation levels returned to normal, high levels of blood clotting were found among patients with persistent COVID symptoms, compared to healthy controls, in a recent study by the Royal College of Surgeons in Ireland (RCSI) at the University of Medicine and Health Sciences in Dublin.

“Millions of people are already dealing with the symptoms of Long COVID syndrome, and more people will develop Long COVID as the infections among the unvaccinated continue to occur. It is imperative that we continue to study this condition and develop effective treatments,” said study co-author Dr. James O’Donnell.

Researchers found that patients with persistent symptoms of Long COVID continue to have higher measures of blood clotting, and those measures are higher if the patient was hospitalized during their infection. Pictured, a clinician cares for a COVID-19 patient in the Intensive Care Unit (ICU) at Providence St. Mary Medical Center amid a surge in COVID-19 patients in Southern California on December 23, 2020 in Apple Valley, California. (Mario Tama/Getty Images)

In previous work, the same group of researchers studied dangerous clotting in patients with severe acute COVID-19. In the latest study, published in the Journal of Thrombosis and Haemostasis, researchers examined 50 patients with Long COVID to understand if abnormal blood clotting is involved.

The authors noted that autopsies have shown that inflammation in the cells that line the heart and blood cells, as well as blood clotting in the vascular system triggered by the immune system play key roles in acute COVID-19. They hypothesized that activation of the endothelial cells that line the heart and blood vessels may contribute to Long COVID.

They found that patients with persistent symptoms of Long COVID, such as fatigue and reduced physical fitness, continue to have higher measures of blood clotting. These clotting markers were higher in patients who required hospitalization for their initial COVID-19 infection, but even those who managed their illness at home still had persistently high clotting markers.

“Because clotting markers were elevated while inflammation markers had returned to normal, our results suggest that the clotting system may be involved in the root cause of Long COVID syndrome,” said the study’s lead author, Dr. Helen Fogarty.

“Understanding the root cause of a disease is the first step toward developing effective treatments,” said O’Donnell, who directs the Irish Centre for Vascular Biology at RCSI and is Consultant Hematologist for the National Coagulation Centre at St James’s Hospital in Dublin.

The research received funding from the Welcome Trust, Health Research Board Irish Clinical Academic Training program, and the HRB-funded Irish COVID-19 Vasculopathy Study. It also received support from the 3M Foundation to RCSI University of Medicine and Health Sciences in support of COVID-19 research.

Edited by Kristen Butler and Judith Isacoff