Researchers in the UK are probing a potential link between blood clots and long-term symptoms post a COVID infection, and whether treatment of blood thinners may help reduce long COVID conditions, media reports said.

Long COVID is defined as having new or ongoing symptoms four weeks or more after the start of the disease. The symptoms, which include fatigue, shortness of breath, loss of concentration and joint pain, may last up to months and even more than a year.

Previous studies have pointed out that a COVID infection increases the risk of blood clots. Infected people have a greater risk of related conditions including stroke, heart attacks and deep vein thrombosis, the Guardian reported.

Prof Ami Banerjee from University College London is leading a study called Stimulate-ICP, where 4,500 people with long COVID will be divided into four groups in which participants are allocated usual care, antihistamines, an anti-inflammatory or an anti-clotting drug for three months.

"That will allow us to say whether that improves the fatigue and other outcomes of people with long COVID," Banerjee was quoted as saying. A study by researchers at the University of Cambridge, called Heal-COVID, involves people who were hospitalised with COVID and aims to identify treatments that may help to prevent or reduce ongoing symptoms, the report said.

"Heal-COVID is not a study treating people with long COVID, we are aiming to prevent things getting to that point," said chief investigator Prof Charlotte Summers from Cambridge. The team has recruited 1,118 participants, with one arm of the trial involving participants receiving blood thinners.

"The trial included anticoagulants as there was thought to be an increased number of large blood clots occurring in the post-hospital phase of the illness rather than micro clots," Summers said. Further, a team from the University of Leicester is also probing the issue of clotting, the report said.

The post-hospitalisation COVID-19 study is looking at whether people with ongoing symptoms after hospitalisation have chronic thromboembolic pulmonary hypertension. If this is found, it would be strong evidence that micro clots are a substantial problem, Chief Investigator Chris Brightling, Professor of respiratory medicine at the University was quoted as saying.

"Whereas if we don't see that, that doesn't exclude the possibility that, obviously -- certain individuals get clots -- but it would make it less likely that it's intrinsically a major problem," he said.