Lab Values, part 16: White Blood Cells (WBCs) & Differentiation

Hi, I'm Meris, and in this video, I'm going to be talking to you about the lab values white blood cell count along with differentiation. Let's go ahead and get started. So first up, let's talk about white blood cell count. And here we're going to talk about the function of white blood cells. It's very straightforward in this case, thank goodness. White blood cells are incredibly important in fighting infection. They're a really key player in your immune system, and they are important for being on patrol and on the lookout for any kind of pathogen or even for cells of my own body that have gone rogue and need to be destroyed. So that's what the function of white blood cells is. And now when we're talking about the lab value white blood cell count, WBC, I just want to remind you that here we're talking about all white blood cells. We are not separating them or what we call differentiating between them. We are just saying, here's how many there are, okay? And so when we talk about the expected range, again, this is a lab value that's taking place usually as part of a complete blood count. So in this case, we're just counting how many of these there are in my patient's blood using a technique that allows me to estimate that. So the expected range here is going to be that there are 5,000 to 10,000 cells per cubic millimeter, okay? And cubic millimeter, it's a measure of volume. So you can also think of it as one milliliter cubed, okay? So it's a very small amount, very large amount of cells, and a very small amount of space. And that's good. That's what we want. That's what we expect. We expect to see that there's kind of this range depending on what's going on in my body. Maybe I have more or less white blood cells at a given point, but they're in this range. And that's good. We're happy about that.

Now, what happens if my white blood cell count is low? Well, we call this leukopenia, and this is going to be-- in this case, we actually take it a little bit lower. We say that this is going to be less than 4,000 per cubic millimeter. Because again, we do want to have just a little bit of wiggle room there for some normal physiological processes before we go getting concerned about the low white blood cell count. Again, this is less common because usually the abnormality is going to be that I have that high white blood cell count. Now, in this case, some possible causes would be autoimmune conditions. So if I have an autoimmune disorder, then my immune system is not functioning in the correct way, which may mean that I have too few white blood cells. I could also have bone marrow suppression. And usually, again, this is related to drugs that I am taking, not illicit substances, but medications. Maybe I have an autoimmune disorder and you have me on an immunosuppressant, which is going to suppress my immune system. Maybe I have a form of cancer and you have me on a bone marrow suppressant. So whatever the reason is, if I am suppressing the bone marrow, then I'm not going to have as many white blood cells as I would anticipate otherwise. And then drug toxicity is also possible. And I want to throw in there, too, some cancers as well. You may see somebody with a low white blood cell count in some cancers.

Now, what if I have too many white blood cells? Well, we call this leukocytosis. This is the condition of having too many cells that are white. Leuko means white, cyto means cell. So in this case, why? Well, the big reason is going to be infection, right? The whole point of my white blood cells is for them to fight infection. So if there's more of them than expected, it's likely that this is related to fighting an infection. I can also have leukocytosis if I have inflammation. So again, inflammation is kind of nonspecific. It doesn't tell me what's going on. I can have inflammation due to autoimmune conditions. I can have inflammation due to having surgery recently. I can have inflammation due to some cancers. So there's a lot of different things that could cause this, but just in general, any sort of inflammatory process in my body puts me at risk for elevated white blood cells or leukocytosis.

Now, I want to talk to you about something different. This is something called differentiation. And you've seen this. If you've ever seen a lab value-- a lab test - I'm sorry - that says CBC with diff or with differential. What they're talking about is I don't want you to just count the white blood cells. I want you to count the white blood cells. And then I also want for you to differentiate between them. So we have a bunch of different types of white blood cells, and they do different things in our bodies, and we have a different proportion of them all of the time. So it's important that when we're talking about this, we remember we're talking about multiple different types of cells that we are counting, and we expect there to be some variation. So we have these ranges for what percentage of the total white blood cell count they should be making up. So here are these percentages, and we're just going to put them on the screen for you. I'm not going to go through every single one, but I want to point out a couple of things. We have them listed here in order of most to least occurring, most prevalent, most commonly found, all the way to the least common cells that we see when we look at a patient's blood. So that's important. You can see the ranges there.

Neutrophils. Neutrophils are incredibly important. These are the first responders of my white blood cells. So I expect that I'm going to have 40 to 60 percent of my white blood cells be neutrophils. I need to have those first responders who are out on the look and they're saying, "Hey, do you belong here? Hey, hey, let me see. Let me see your molecule that tells me that you belong to this body," right? Because I need to quickly neutralize a threat. So when I have an elevated neutrophil level, this is likely due to an acute infection. This is something right now. I've got a bacterial infection that my body is fighting right now in this moment. It's going to elevate my neutrophils, and that's something to be on the lookout for. We do have a cool chicken hint here to remind you that neutrophils are the first to neutralize, neutralize the threat. Okay, now lymphocytes, these are incredibly important to remember when we are talking about people who have chronic bacterial or viral infections. My neutrophils, these are the first responders, but that doesn't mean that they are the only ones involved, right? They're going to peter out after a while when this is not an acute infection anymore. They're going to pass along the management of this infection to the lymphocytes. And the lymphocytes are going to be elevated if I have a chronic bacterial or viral infection. Monocytes, these are related to protozoal and viral infections, tuberculosis, and chronic inflammation.

Eosinophils, these are related to allergic reactions or parasitic infestations. So that's important to know. These guys tell us if they can be related just to allergy, but it can also be related to things such as parasitic worms. So that's an unusual one to pay attention to. And then lastly, basophils. Basophils, these respond in cases of allergic reaction, sometimes in case of leukemia. But the cool chicken we have here to remind you is that with basophils, you might need Benadryl, both of them starting with a B, to help you remember that it is tied into allergy. But I hear you looking at this chart and you're saying, "Oh my God, Meris, what's the point?" Here's the point. The point is that it goes from most prevalent to least prevalent, and you've got your acute and your chronic infection. Those are like the big ones that I want to call your attention to. And I hear you saying, "But how am I going to remember which order they go in from most to least common?" And I have some great news for you. We figured that out for you. We've got a cool chicken hint here, which is never let monkeys eat bananas. That tells you starting with most prevalent all the way down to least, neutrophils, lymphocytes, monocytes, eosinophils, and basophils. So that way you can remember this important information about differentiation.

Now, what's the point? Why are we differentiating? Well, if you have me in your ER and I say, "I'm not feeling well, X, Y, Z is the problem," and you run my CBC and the white blood cells come back elevated, great, that tells me we've got something, right? It doesn't tell me what's going on, and it doesn't help me narrow it down anymore. So if you have an elevated white blood cell count, this should trigger the lab, if we added with differential, to differentiate between these so that we can say, "Hey, how many?" This is done by literally looking under a microscope. And I want to explain something to you called left shift, in case you ever hear this. When we talk about white blood cells, we often care a lot about whether these are mature cells or immature cells. If they are immature cells, this tells me that my body is working very hard to create these right now because it's mounting a response to something that is happening. The infection is causing my body to respond right now. So that's why I have these elevated amounts of immature or juvenile white blood cell counts. If I have a ton of older, mature ones, ones that are on their way out, that gives me different information. We're not trying urgently to mount a response. We've been there, done that. These are now mature cells.

So when this was an emerging technology, these were all done manually. They were called manual differentials, where they were done by looking under a microscope. And literally, someone would stain a microscope slide, and they would go through and count in a certain size space under the microscope, how many of these different cells they see. Well, I don't want to take my eyes off of the microscope to write down, okay, I've got one eosinophil. Okay. I've got two neutrophils. I don't want to do that, right? So instead, they had this little machine that was a counter where you could just push and it would start with-- you would have two different types. You would have one that has the differentiation, and one of them where they're actually going to look at, is this a juvenile cell or is this a mature cell? When we do that, we're going to be pushing buttons saying, okay, neutrophil, neutrophil, basophil, neutrophil, lymphocyte, monocyte, whatever, or they're pushing buttons on the immature to mature. This information could then be plotted on something called a bell curve, which is going to show us the normal distribution and the distribution that our patient has.

So we expect that most of the white blood cells are going to fall in that middle somewhere. They're going to be not immature and not mature. They're just kind of hanging out. And we expect there to be not very many immature and not very mature cells either. So we'll have that nice bell curve to the distribution of the maturity of these cells. However, if as we're doing this manual differential, I'm seeing, oh, immature, immature, immature, it's going to change the shape of that bell curve and it's going to create what's called a left shift, meaning that the bell curve has shifted over so that the height of it is more towards the left, indicating that there are more immature white blood cells in circulation. So the reason I mention this to you is because people use this term all the time and have no clue what it means. They just know that-- or where it comes from, I mean. They just know that it means this person is actively mounting a response. But now you know that left shift refers to the leftward deviation of the bell curve when it comes to the maturity of those white blood cells.

All right, I'm so glad you stayed until the end because I am going to test your knowledge of key facts provided in this video with some quiz questions. A provider remarks on the left shift in the patient's white blood cell differential. The nurse understands this to mean what?

The patient is producing more immature white blood cells than usual to help fight an infection.

Which white blood cell value does the nurse expect to see elevated in a patient who has a chronic bacterial infection?

Lymphocyte.

All right, that is it for this video. I do hope you learned something. Thanks so much for watching and happy studying.