Study Suggests Blood Clots are Part of Long COVID Puzzle

Sept. 1, 2023 – A new study links long COVID cognitive problems such as brain fog to higher levels of proteins known to be involved with the way that blood clots. 

Some scientists have noted the possibility that tiny blood clots restrict blood flow to vital organs as part of a COVID infection. The authors of this latest study wrote that their findings show the need for exploring the link between blood clotting and long COVID.

The study, conducted in the United Kingdom, was published this week in the journal Nature Medicine. Researchers reviewed blood tests from 1,837 people who had been hospitalized with COVID-19. The average age of people in the study was 58 years old, and 58% were men.

Participants underwent formal cognitive testing at six and 12 months following hospitalization. They also reported their thoughts on their brain function after having COVID-19. 

People with elevated levels of proteins at the time of their COVID-19 infection later experienced persistent and serious problems with memory, concentration, and thinking. One of the proteins identified at elevated levels in affected long COVID patients is called fibrinogen, and the other is a protein fragment called D-dimer.

“Both fibrinogen and D-dimer are involved in blood clotting, and so the results support the hypothesis that blood clots are a cause of post-COVID cognitive problems,” said study author and University of Oxford biomedical researcher Max Taquet, PhD, in a statement. “Fibrinogen may be directly acting on the brain and its blood vessels, whereas D-dimer often reflects blood clots in the lungs and the problems in the brain might be due to lack of oxygen. In line with this possibility, people who had high levels of D-dimer were not only at a higher risk of brain fog, but also at a higher risk of respiratory problems.”

People with elevated D-dimer levels also reported difficulty at work or holding a job.

There was no relationship found between elevated fibrinogen and non-cognitive long COVID symptoms including fatigue, shortness of breath, problems exercising, pain, depression, or anxiety. 

Researchers did find a link between elevated D-dimer levels, fatigue, and shortness of breath.

Understanding the causes of brain fog and other cognitive problems that affect people with long COVID is an important step toward finding treatment or prevention, the authors wrote. For example, further study could include brain imaging that might indicate whether it would be helpful to give blood thinning medication during an active COVID infection, the authors suggested. 

They noted that elevated protein levels were not related to people having cognitive problems prior to COVID infection.