Patients with symptoms of long Covid syndrome continue to have higher measures of blood clotting, which may help explain some of their persistent symptoms, such as fatigue and reduced physical fitness, a new study led by RCSI researchers has found.

Previous work by the same group had looked at the dangerous clotting observed in patients with severe acute Covid-19. However, far less is known about long COVID syndrome, where symptoms can last weeks or months after the initial infection has resolved.

This latest study assessed 50 patients with symptoms of long COVID syndrome to better understand if abnormal blood clotting is involved. The researchers found that clotting markers were significantly elevated in the blood of patients with long Covid compared with healthy controls.

While these clotting markers were higher in patients who required hospitalisation with their initial Covid infection, the study also found that even those who were able to manage their illness at home still had persistently high clotting markers.

It was observed that higher clotting was directly related to other symptoms of long Covid, such as fatigue and reduced physical fitness. Even though markers of inflammation had all returned to normal levels, this increased clotting potential was still present in long Covid patients.

“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,” explained the study’s lead author, Dr Helen Fogarty, ICAT Fellow and PhD student at the RCSI’s Irish Centre for Vascular Biology.

According to consultant haematologist and director of the Irish Centre for Vascular Biology, Prof James O’Donnell, understanding the root cause of a 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. It is imperative that we continue to study this condition and develop effective treatments,” he said.

Details of these findings are published in the Journal of Thrombosis and Haemostasis.