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Blood clots may cause ‘brain fog’ after COVID

Published: 04 September 2023

A study has found blood clots may be a cause of cognitive problems such as ‘brain fog’ in patients after COVID-19.

The study was supported by two NIHR Biomedical Research Centres: Leicester and Oxford Health. It was funded by MQ Mental Health Research and the Wolfson Foundation.

Looking for ‘biomarkers’

Researchers from the University of Oxford analysed blood tests from 1,837 people hospitalised with COVID-19. They were looking for potential ‘biomarkers’ associated with cognitive problems that the patients experienced later. The symptoms included serious and persistent problems with thinking, concentration and memory.

The researchers identified two separate profiles of biomarkers. The first was having a high level of a protein called fibrinogen. The second was a raised level of a protein fragment called D-dimer.

On the discovery of patients with high levels of the two proteins, Dr Max Taquet from the University of Oxford 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.”

Debilitating symptoms

The participants involved in this research are part of the PHOSP-COVID (Post-hospitalisation COVID-19) study. It is based at the University of Leicester. Their memory was measured six and 12 months after hospitalisation. Researchers used an objective test and asked them about their own subjective view of their memory.

Dr Rachael Evans, Associate Professor, Department of Respiratory Sciences at the University of Leicester, said: “Large detailed studies such as PHOSP are vital if we’re to understand the different ongoing, and often debilitating, symptoms that people are continuing to experience post-COVID.”

Read the full paper in Nature Medicine.

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