The study, published in the journal Neurology, assessed blood samples taken from 47 patients with mild, moderate, and severe COVID-19 in the course of their hospital stay.
Researchers, including those from the University of Gothenburg in Sweden, analysed these samples by means of highly sensitive biomarkers for brain injury, and compared the results with those from a healthy control group comprising 33 people matched by age and sex.
In even moderate COVID-19 cases, they found that measuring a blood-based biomarker for brain damage is possible.
The scientists found that a marker, known as glial fibrillary acidic protein, or GFAP, is normally present in star-shaped neuron-supportive cell type in the brain called astrocytes, but leaks out in the event of injury or overactivation.
They also found a second biomarker called NfL (neurofilament light chain protein), which is normally found inside the brain's nerve outgrowths, but leaks out into the blood if they are damaged.
According to the study, elevated concentrations of NfL in the blood's plasma component was found in most of the COVID-19 patients who required ventilator treatment.
The researchers said there was a marked correlation between how much the NfL concentration rose and the severity of the disease.
According to the scientists, some people infected with the coronavirus SARS-CoV-2 get only mild, cold-like symptoms, while others become severely ill and require hospital treatment.
Among the latter, they said patients sometimes show obvious signs of the brain not functioning as it should.
An increase in one of the biomarkers took place even with moderate COVID-19, such as in hospitalised patients not in need of ventilator support, the scientists said.
"The increase in NfL levels, in particular, over time is greater than we've seen previously in studies connected with intensive care, and this suggests that COVID-19 can in fact directly bring about a brain injury," said study co-author Henrik Zetterberg from the University of Gothernburg.
"Whether it's the virus or the immune system that's causing this is unclear at present, and more research is needed," Zetterberg said.
Magnus Gisslen, another co-author of the study from the university said blood tests for biomarkers associated with brain injury could be used for monitoring patients with moderate to severe COVID-19.
"It would be highly interesting to see whether the NfL increase can be slowed down with new therapies, such as the new dexamethasone treatment that's now been proposed," Gisslen said. VIS VIS