When your head takes a hit, your brain is subjected to shear forces—without any of the structural damage you can see on a CT scan or an MRI. But they also release a number of proteins into the cerebral spinal fluid. About one in a thousand of those proteins crosses the blood-brain barrier to enter the bloodstream. The more damage, the higher the blood protein concentration. Tau is one such complicated protein. Made by neurons, it gets tangled into snarled plaques in the brains of people with Alzheimer’s and chronic traumatic encephalopathy, a neurodegenerative disease linked to the premature death of NFL players and professional boxers. And it’s a known biomarker for concussions.
In a paper published earlier this month in Neurology, Gill and her colleagues used this method to track tau levels in over 600 collegiate athletes over the course of two sports seasons. Gill’s team found that concussed players had elevated levels of tau protein, over both other athletes, and over a non-athlete control group, often for days after the injury. And as they monitored different athletes’ recoveries, they saw that tau levels closely predicted not only the severity of the injury, but the amount of time needed before the players could return to activity. What they’d discovered was a blood test for concussions, more sensitive and less biased than any human evaluator.