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Diagnosing strokes with lab tests
- [Voiceover] There's three main steps in diagnosing strokes. Step one is to get a good history from the patient and to do a physical exam on them to check for neurological symptoms that the stroke might have caused. Step two is to do some imaging, like CT scanning or MRI to directly look at the brain to see what's going on with it's blood supply. And this is actually probably the most useful step in diagnosing stroke. Now, step three, the focus of this little chat that we're gonna here, is lab testing. So things like blood work. And you might be thinking, "Well, how can blood work diagnose a stroke?" And you'd be on to something because blood tests alone can't diagnose strokes, but what they can do is look for conditions that might be the cause of the stroke. And they're also really helpful in excluding things that may be mimicking a stroke, like, say, abnormally low blood sugar levels, which can sometimes cause symptoms that look like stroke symptoms. So what sorts of blood tests are usually ordered? Well, a complete blood count, or a CBC, is one of them. So this is a test to check that you have a normal amount of red blood cells, white blood cells, and platelets in your blood. Because sometimes strokes can happen as a result of certain blood conditions. So, for example, say you had too many red blood cells in your blood, and that's a condition called polycythemia. Or say you had too few platelets in your blood which is a condition called thrombocytopenia. You'd be at a higher risk of stroke and that's because these conditions, and ones like them, they alter the rate at which your blood clots. So you can imagine that if your blood clotted too much for whatever reason, you'd be at a higher risk for getting a clot stuck in a cerebral blood vessel and having an ischemic stroke. And if your blood clotted too little then you'd be at a higher risk of having a hemorrhagic stroke, right? So maybe if a blood vessel had some trauma to it and the hole wasn't able to seal up and stop blood from leaking out, then you'd be at a high risk for hemorrhagic stroke. You might also get your electrolytes and your blood sugar checked because this might reveal some conditions that look like a stroke, but aren't. So, for example, hyponatremia, or sodium that's just too low in the blood, can cause impaired electrical activity in the brain and this can cause seizures and stroke-like symptoms that might look like a true stroke. So it's important to rule that out. Oh, and the electrolyte check can also give you an idea of whether there's some underlying kidney disease in the patient as well. Because the kidneys are responsible for maintaining our electrolyte concentrations in our blood at the proper levels. So if our electrolytes are out of whack then we check to see if the kidneys are out of whack. And kidneys that are not functioning very well can predispose you to stroke. And now this hypoglycemia, or blood sugar that's way too low, right? Glycemia refers to glucose, which is blood sugar. This can also look like a stroke and it can even result in symptoms like weakness or numbness on one side of the body or trouble speaking and vision problems. Sounds familiar, right? It sounds a lot like a stroke so it's important to get the blood sugar checked so that if it is just a hypoglycemic event that can be corrected and stroke can be somewhat ruled out. And one more thing, the glucose check can give you an idea of whether or not the patient has diabetes, which increases your risk of stroke. Now, what other blood tests? Well, you could do coagulation studies to check if the patient has an underlying blood clotting problem. And this is slightly different to what we talked about earlier. Here we're talking about testing for problems with your actual blood clotting proteins that are made in your liver. The proteins that are primarily responsible for forming blood clots. Whereas earlier we were talking about conditions of your blood cells that can predispose you to clots. So before we were talking about blood cells and now we're talking about the blood clotting proteins. So this one's interesting. I mean, these proteins are responsible for making your blood clot, so if there's a problem with them, for example if they cause clots too easily, you can imagine that increases the risk of a clot traveling up to the brain and causing a stroke. Or maybe when they form clots they don't break up when they're supposed to. We have a nice mechanism in our bodies to break up clots in certain situations, so if that system malfunctions for some reason that would increase your risk even higher, right? And on the flip side, let's say, actually, they don't even form clots properly then could predispose you to likely a hemorrhagic stroke. Another important blood test to do is one for certain proteins that may have come from your heart muscle, like troponin T or troponin I or CKMB. These are proteins that might sort of leak out of your heart muscle cells when they get injured. So, you might be thinking, "Well, what does heart muscle injury "have to do with a stroke?" Well, for one, problems with your heart might give you symptoms that look like a stroke, so it's important to check if there is underlying heart muscle injury that's actually causing your symptoms. And for two, it turns out that there's an association between cerebral blood vessel disease of the brain and coronary artery disease of the heart. And that's because the same underlying process, atherosclerosis, may have caused them both. So it's important to test for these little heart muscle proteins because they could point to existing heart disease in addition to the possible stroke that we're trying to diagnose. And the last blood test I'll mention is a toxicology screen, or a tox screen. That's probably how you heard it on Law & Order or CSI. And this is mainly to identify patients that might be a little intoxicated with any drug or alcohol and who might be having symptoms or behavior mimicking stroke syndromes. So it's really a test to rule out intoxication or look for any drugs in the blood that might be associated with a risk of stroke. So those are some of the more common blood tests that are done in diagnosing a stroke.