Covid-19 patients face higher risk for blood clots months after infection

WASHINGTON: People infected with Covid-19 are at increased risk for potentially life-threatening blood clots in their legs for up to three months after catching the virus, a study published Wednesday by the BMJ found.

In addition, they have a higher risk for developing dangerous blood clots in their lungs, or pulmonary embolisms, up to six months after infection, reported United Press International (UPI).

Those with severe Covid19 and/or underlying health conditions such as heart disease and high blood pressure were at the highest risk for developing virus-related blood clots, including deep-vein thrombosis, which occurs in the legs, the researchers said.

“Covid-19 is a risk factor for thrombosis and bleeding, with the highest risk in more severe patients,” study co-author Anne-Marie Fors Connolly told UPI in an email.

“Persons who are at increased risk are those with a more severe form of Covid-19, or those that need hospitalisation or intensive care,” said Fors Connolly, a clinical microbiologist at Umea University in Sweden.

Previous studies have indicated that people with severe Covid-19 are prone to developing blood clots.

These blood clots may be caused by rogue antibodies, or immune cells that develop in response to the virus, research suggests.

They can occur early on in the course of disease, or may develop months after infection, leading to long-term heart and lung damage, studies have found.

For this study, Fors Connolly and her colleagues used national health registries in Sweden to identify more than 1 million people with confirmed Covid-19 diagnosed between Feb 1, 2020, and May 25 of last year.

They compared their risk for deep vein thrombosis, pulmonary embolism and bleeding disorders to that of more than 4 million people who had tested negative for the virus, they said.

Those with Covid-19 have a five-fold higher risk for deep vein thrombosis, a 33-fold higher risk for pulmonary embolism and a nearly twofold higher risk for developing bleeding disorders in the 30 days after infection, compared with those who do not have the virus, the data showed.

Of the 1 million patients with Covid-19, 401, or well under 1 per cent, developed their first deep vein thrombosis after infection, while 1,761 had their first pulmonary embolism after infection with the virus, the researchers said.

In comparison, during the study period, 267 of the uninfected patients had their first deep vein thrombosis and 171 had their first pulmonary embolism, according to the researchers.

In addition, among the infected patients, 1,002 had their first bleeding-related disorder after getting the virus, the data showed.

“The virus that causes Covid19 has been shown to infect cells that line blood vessels and can have a direct impact on these with an increased risk of thrombosis,” Fors Connolly said.

“Another way it increases the risk of thrombosis is by causing a hyper immune response, which impacts the coagulation system,” she added.

Persons who are at increased risk are those with a more severe form of Covid-19, or those that need hospitalisation or intensive care.

Anne-Marie Fors Connolly