Dr Max Taquet and colleagues from the University of Oxford, along with the University of Leicester looked at blood tests from 1,837 people who had been hospitalised with COVID-19 to find potential proteins (biomarkers) associated with subsequent cognitive problems, with symptoms including serious and persistent problems with thinking, concentration and memory.
In a new paper published in Nature Medicine, they identified two separate profiles of biomarkers. The first was having a high level of a protein called fibrinogen, and the second was a raised level of a protein fragment called D-dimer. Other aspects of the profiles suggested they are likely to reflect blood clots. The main findings were replicated using electronic health records in a separate population.
Dr Taquet said: '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. 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.