Blood Test for Concussions

Can a blood test help diagnose a concussion?

On February 14, 2018, the U.S. Food and Drug Administration (FDA) approved a blood test for use in the diagnosis of concussions

Scientist with blood tube
Andrew Brookes / Getty Images

Concussions are the perfect example of how the practice of medicine is both art and science. For decades, the mild traumatic brain injury (TBI) known as a concussion was not very well understood. How brain tissue was affected, the long-term effects, treatment, and even a clear understanding of signs and symptoms really didn't begin to solidify until the end of the 20th century.

Contact sports, particularly professional football, and military combat operations had a large impact (no pun intended) on the medical understanding of concussive injuries, especially how repetitive blows to the head caused damage to brain tissue. As the dangers of concussion became clearer, healthcare providers searched for clarity on how to recognize it.

How the Blood Test Works

The blood test is called the Banyan Brain Trauma Indicator and it measures the levels of proteins, known as UCH-L1 and GFAP, that are released from brain tissue into the bloodstream. When measured within 12 hours of an injury, the levels of these proteins can help determine whether or not a patient could have lesions on the brain detectable with either a CT scan or an MRI.

Mild traumatic brain injuries—concussions—often do not show lesions on images of the brain. Worse, the massive amount of radiation exposure necessary to obtain a CT scan can have negative consequences over time. The risk is worth it to diagnose potentially life-threatening injuries, but unnecessary CT scans should be avoided.

What the Blood Test Does

The Banyan Brain Trauma Indicator helps doctors decide whether or not to do the CT scan. In research used by the FDA to approve the test, it correctly predicted that patients would have lesions detectable on their CT scans 97.5% of the time. The test correctly predicted that patients would not have lesions detectable by CT scan 99.6% of the time. 

Therefore, when used as a first line diagnostic tool, the test helps to rule out those patients who don't need to endure the radiation of a brain CT scan. The test is fast enough to be used before the CT scan without causing significant delays.

What the Blood Test Doesn't Do

It does not diagnose concussions. It's important to understand the difference, because it's not like doctors can pull out some sort of doohickey that looks like a glucometer and diagnose concussions with a drop of blood on the sidelines of the big game.

At least, not yet.

This test is not conclusive by itself. It's not a panacea. However, it will help doctors navigate patients that don't have very severe traumatic brain injuries. Using this test along with more conventional methods of diagnosis—Glasgow Coma Scale and other neurological assessments—will help doctors decide whether to subject a patient to radiation. That's not a small thing.

How Concussions Are Diagnosed

For many years, concussions had two criteria for diagnosis:

  1. The patient is knocked unconscious temporarily.
  2. The patient doesn't remember what hit him.

The third, sometimes unspoken, criteria for diagnosis was that it had to be trauma related. The patient had to get smacked on the noggin in order for us to even consider concussion as a diagnosis. That's really the only standard that still exists. It wouldn't be a concussion without a bump on the head.

The Veterans Affairs/Department of Defense clinical practice guideline for the management of concussion-mild traumatic brain injury does a great job of laying out the modern steps for diagnosing concussions. The most important thing to remember is that this is a diagnosis of exclusion. The idea is to rule out (to make sure) that the patient does not have a significant traumatic brain injury.

If she doesn't have a potentially life-threatening traumatic brain injury, then the patient could have a concussion. Some of the concussion signs and symptoms used to determine severity include:

  • Progressively declining level of consciousness (typically using the Glasgow Coma Scale)
  • Progressively declining neurological exam (performed by a healthcare provider)
  • Unequal pupils (a significant sign of traumatic brain injury)
  • Seizures (especially if the patient has never had them before)
  • Repeated vomiting
  • Neurological deficit: motor (can't move correctly) or sensory (can't feel touch correctly)
  • Double vision
  • Progressively worsening headache
  • Unable to recognize people or disoriented to place (in sports, the patient might not remember the name of the opposite team)
  • Slurred speech
  • Unusual behavior (personality changes, for example)

If a patient presents with any of these criteria, the potential for a significant traumatic brain injury exists and the patient would typically be given a CT scan to look for injuries that can be treated with surgery (subdural or epidural hematoma, for example). 

The biggest difference between traditional and modern assessments is that patients no longer have to get knocked out for healthcare providers to be concerned about concussions. Indeed, the medical profession continues to learn just how soft a blow to the head can be and still cause injury.

How a Blood Test Can Help

Some of the signs and symptoms above can exist in patients with very minor traumatic brain injuries. Even by concussion standards, they can be minor.

That's where the blood test comes in.

In patients with a history of a whack to the dome who just have a headache or vomiting, but don't exhibit any of the other signs listed, a CT scan might be warranted and might not. Until the development of a blood test, that decision fell to the healthcare provider to make without any supporting evidence one way or the other.

Now, the clinician can test for concussion biomarkers in the bloodstream. If the test is negative, it means that 99.6 times out of a 100, the patient will not have anything visible on the CT scan. That gives the doctor a clear path to focus the assessment on less invasive tools. It doesn't mean this patient isn't in the 0.4% that will have something visible on CT scan, but a good healthcare provider will still observe the patient to make sure everything is progressing appropriately.

The Future of TBI Blood Testing

This is likely just the beginning. The use of certain proteins as biomarkers was studied for several years before the introduction of the first test. Additional research is likely to focus on the levels that will tell us when a patient is in significant danger of a traumatic brain injury. Biomarkers will also play a part in identifying when patients are healed.

Despite the fact that a drop of blood on the sidelines isn't how it's done right now, it doesn't mean that's not the future of biomarker blood testing. Imagine a team doctor in professional sports or a combat medic on the front lines being able to immediately test an injured soldier or player to determine if there's been a concussion or not.

Right now, the decision to put a patient back into the very situation that led to the injury, a decision with significant pressures on the caregiver, is made based on a best guess. The clinician often uses pregame concussion testing to determine a baseline neurological functionality, then retests the player or the soldier at the point of injury. If the patient doesn't do as well the second time around (under his or her own pressure to perform) he or she might be removed from the field and sent for further treatment. 

Blood testing could become a marker for reentry to the game or the battlefield. The uses remain to be seen.

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