Over the past couple of days a number of prominent media outlets published a story about the first ever FDA-approved blood test to diagnose or detect a concussion.
New York Times: Concussions can be detected with new blood test approved by FDA
The problem with these sensationalist headlines that are intended to pique your interest can mislead the public.
But, the question remains…
Can a blood test diagnose a concussion?
In short, the answer is no. Not yet.
There have been many studies on blood “biomarkers” in the past few years. All of them had the same goal: try and find a blood test for concussion.
The theory is that because the central nervous system (CNS) has a completely separate immune system (due to blood brain barrier (BBB) permeability only allowing certain things through), we should not see any “brain-specific proteins” in the systemic circulatory system (i.e., blood).
In severe forms of brain injury, these proteins have been found in blood. So naturally, researchers began looking to see if we would see the same type of thing in mild brain injuries (i.e., concussion). However, there are a couple of significant issues which have made this a little more difficult than the media is leading us to believe.
Issue 1: Concentration – Simply put, although we find these proteins in moderate and severe brain injuries, there is much more damage to the tissues of the brain, which results in a lot of these proteins being released. But in concussions, the structural damage is minimal (if at all), and therefore, you are not going to get the same amount of this protein. Small amounts floating around your bloodstream are very difficult to find.
Issue 2: Timing – Anything that is in systemic circulation system will be taken up by the liver and broken down, or possibly attacked by the immune system because it will be seen as foreign. Therefore, there is an inherent issue with timing; or accessing the blood in the right time frame to ensure adequate concentration for detection.
Issue 3: Tissue Strength – What has more tensile strength: the neural issues of the brain or the blood vessels/blood brain barrier?
- If brain vasculature is stronger you could get a concussion without any proteins being found in the blood. The injury would happen in the brain, but nothing would be released into the bloodstream. This would result in a false negative.
- If neural tissue is stronger you could get proteins released into circulation without a concussion injury; resulting in a false positive.
Issue 4: No “gold standard” in concussion diagnosis – a gold standard is a test or procedure that is 100% accurate. Whenever you are trying to come up with a new diagnostic test, you need a way to examine the new test against the gold standard to see how good it is.
For example, the gold standard test to see if a ligament is torn in the knee is arthroscopic surgery (actually going in with a camera to see the torn ligament with your own eyes). Once you have the gold standard you can compare how good other “tests” are at finding the same thing (ex. MRI, X-rays, hands-on examination techniques, etc.).
The problem with concussion is that there is no gold standard to compare to. This means that we can never confirm how “accurate” a test is without first knowing if there has truly been a concussion.
Not surprisingly, studies in this domain have yielded very mixed results. Further, some of these proteins are found in peripheral tissues (muscles, bones, fat and joints) and are released during regular exercise. This adds to the debate.
So, what about the FDA-approved blood test?
In the case of the FDA-approved blood test, these particular biomarkers (UCHL1 and GFAP) have been found to correlate with positive imaging findings for bleeds in the brain.
This makes sense considering an active bleed is a perfect opportunity for fluids to mix and brain-specific proteins to make it into systemic circulation (blood). But, the utility of this test has more to do with helping an emergency room physician determine if they need to order a CT scan to check for a bleed than it does for making a diagnosis of concussion.
Overall, this is a step in the right direction as it has the ability to cut down on both harmful radiation as well as expensive CT scans. But, in terms of diagnosing a concussion, we may have been mislead by the headlines.
These stories serve as another lesson about what we read, and reading more than just the headline. Concussion is a hot topic, and these sensationalist headlines serve a purpose for the media outlets. We encourage those interested in concussion to dig deeper, follow the experts, and question some of the sources they read to get the full story.
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