High rates of blood clotting linked to symptoms of Long Covid

RCSI researchers seek to explain why some suffer side-effects long after infection cleared

High levels of blood clotting may be the root cause of the symptoms suffered by those with so-called Long Covid, new research suggests.

Developed by millions around the world, Long Covid is a syndrome where people who have contracted Covid-19 continue to suffer side-effects long after the initial infection has cleared.

A study by researchers at the Royal College of Surgeons in Ireland (RCSI) of 50 patients with Long Covid found a higher rate of blood clotting than in healthy people.

Total doses distributed to Ireland Total doses administered in Ireland
9,452,860 7,856,558

In particular, the researchers observed that higher clotting rates were directly related to symptoms such as reduced physical fitness and fatigue. Even though markers of inflammation had all returned to normal levels, this increased clotting potential was still present in Long Covid patients.


Led by researchers from RCSI University of Medicine and Health Sciences, the study is published in the Journal of Thrombosis and Haemostasis.

Previous work by the same group studied the dangerous clotting observed in patients with severe Covid-19.

However far less is known about Long Covid syndrome whose symptoms can last weeks to months after the initial infection has resolved.

The researchers’ examination of patients discovered clotting markers were significantly elevated compared with healthy controls. The markers were higher in patients who required hospitalisation with their initial Covid-19 infection, but were also persistently high in those who were able to manage their illness at home.

"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 lead author Dr Helen Fogarty of the Irish Centre for Vascular Biology in the RCSI School of Pharmacy and Biomolecular Sciences.

Professor James O’Donnell, consultant haematologist in the National Coagulation Centre in St James’s Hospital, Dublin said that understanding the root cause of the disease is the first step toward developing effective treatments.

“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,” he said. “It is imperative that we continue to study this condition and develop effective treatments.”

Long Covid has continued to concern the medical community throughout the pandemic. With symptoms including shortness of breath, heart palpitations, chest pain and fatigue, recent studies have shown it affects 10 to 15 per cent of people who test positive for the virus.

Earlier this month Anthony Staines, professor of health systems at Dublin City University, warned that Ireland's health service was insufficiently equipped to treat those affected.

“We have a serious capacity problem in the Irish health services for everything,” he told a webinar. “We are not too bad at treating serious acute illness, [but] we are genuinely awful at treating complex, long-term illness of many kinds.”

Mark Hilliard

Mark Hilliard

Mark Hilliard is a reporter with The Irish Times