A new study, published in the Journal of Thrombosis and Haemostasis, has shown that blood clotting is responsible for long COVID syndrome, according to Science Daily.

The study, conducted by researchers from RCSI University of Medicine and Health Sciences, said most patients with long COVID syndrome continue to have higher measures of blood clotting, which explains why they have persistent symptoms, such as reduced physical fitness and fatigue.

Previously, the researchers studied the dangerous blood clotting in patients with severe acute COVID-19, but less is known about the syndrome, in which patients experience the symptoms from weeks to months after the initial infection has resolved.

Long COVID syndrome is estimated to affect millions of people across the world.

For the current study, the researchers looked at 50 patients with symptoms of long COVID to better understand whether it is due to abnormal blood clotting. And they discovered that blood-clotting markers were significantly elevated in patients with long COVID syndrome compared to healthy controls.

The investigators found that the blood clotting markers were much higher in hospitalized patients, but they also found that those who managed their illness at home still had persistently high clotting markers, according to Science Daily.

The team found that higher blood clotting was directly associated with symptoms of Long COVID syndrome.

Lead author of the study Dr. Helen Fogarty said, “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.”

Prof. James O’Donnell of RCSI said, “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,” he added. “It is imperative that we continue to study this condition and develop effective treatments.”