Hey guys, this is Dr. Joel. In this video, I'm going to be talking about the complete blood count or the CBC, which is extremely common in your clinical rotations. You're going to see this over and over again.
So I'm going to have to give it a 5 out of 5 on its importance or its yield. I don't really have enough space in one short video to talk about the entire CBC, so I've broken this topic up into smaller more manageable bite-sized pieces. In this first video, I'm going to be talking about the white blood cells.
And in the second video, I'll be talking about red blood cells. And in the last video, or the third video, I'll be talking about the platelets, and then asking some questions based on what we learned to see how well you can interpret a CBC. Okay?
Let's get started. So first off, what is a CBC? or a complete blood count? Well, it's a very commonly ordered lab or blood panel that gives us some good information about the cell types in a patient's blood. And those cell types are divided into three main types, white blood cells, red blood cells, and platelets.
First up, in our discussion is going to be the white blood cells. And just in case you're brand new to labs, let me real quick run through these columns so it makes a little bit of sense. In the first column is the cell type.
The second column is saying that we're looking at the blood of the patient versus like serum or urine or tissue, something like that. This is at least how my lab reports it. The third column. is the value for that cell type. The fourth column is giving me units, and the last column is my reference range, or my normal range.
So that means that this first row represents the total white blood cells taken from the patient's blood. There was 4.6 times 10 to the third, or in other words, 4,600 white blood cells per microliter. and the normal range for total white blood cells in the blood is between 4.6 thousand up to 11.0 thousand cells per microliter. So that was the first row. What about the next five rows?
Well, these next five rows are individual cell types or cell lines, and they are all white blood cells. You'll notice also that the units are given as a percentage. So of the 4,600 white blood cells per microliter of blood, there was 52.1% of those, 4,600, were neutrophils. And 31.8% of those were lymphocytes, and so on and so on.
And if you add all those percentages up, they should equal 100%, or the total of 4,600 white blood cells. Does that make sense? The first group of white blood cells that I'll talk about are the neutrophils.
And the neutrophils, along with eosinophils and basophils together, make up the polymorphonuclear cells. They have this name because if you look at the nucleus in these cells, The nuclei are multilobulated. What that means is that instead of having a consolidated circular nucleus, the nuclei make little lobules or kind of like globs connected together by what looks like string, but is actually just thin strands of nucleus.
The nucleus of a neutrophil has about two to five of these lobes or lobules. Neutrophils are by far the most abundant type of white blood cell that we see in the blood, and they play a major part in our reaction to acute inflammation, most especially the inflammation as a result of bacterial infection. In fact, the pus that you squeeze out of an abscess is mostly neutrophils.
So given that information, what do you think you might use the neutrophil part of this CBC to diagnose? Bacterial infections. Bacterial infections would cause the neutrophil count to go up. And this is called neutrophilia. I've heard some people call it neutrocytosis as well, but that's not as common.
What are some other things that could cause a neutrophilia? How about acute stress? Or burns? Or leukemia? That's a good one.
Steroid use? Rheumatoid arthritis? Okay, those are a couple. Shifting gears a little bit, what kind of diagnoses do you think would go along with a decreased neutrophil count, also called a neutropenia?
How about a folate deficiency or maybe vitamin B12 deficiency? Aplastic anemia, chemotherapy, maybe they're taking a medication like chloramphenicol or some of the sulfonamides. Those would decrease it as well, all right?
So those are some good reasons for a decreased value. However, most of the time, in my experience, I use this mostly checking for an increased value to help me check for an infection in the patient. I don't often look for a decrease in this value, mostly an increase.
Okay, next on our list to talk about are the eosinophils. And these cells are named eosinophils because they stain very well with the dye eosin, which is a red dye. And so you can see already from this picture that these cells, or this picture of this cell, is slightly more red than the picture of the neutrophils above it.
Alright, so what are some things that might cause the eosinophil count to change, either up or down? Well, you might see an increased count, or an eosinophilia, in an allergic reaction, like a food allergy or a bee sting to someone who's allergic to bees, things like that. Also, parasitic infections is a big one.
Eosinophils contribute to our attack against parasites by surrounding the parasite and then releasing their granules, which have a lot of substances that are toxic to the invading parasite. And there's a link. If you click here, you can watch a video of that happen.
It's pretty cool. What else? What else might cause the... eosinophilia? Well, you can't go wrong if you say leukemia, because certain types of leukemias could definitely increase the eosinophil count, or any other white blood cell for that matter.
Also, you could think of polyarteritis nordosa and some autoimmune disorders. What about eosinopenia, or a decrease in eosinophils? Well, this gets a little bit tricky, just because with eosinophils and basophils, technically, according to my lab at least, 0% is still within normal range.
So it's a little bit difficult to define an eosinopenia or a basopenia. However, if someone really twists your arm, you could say maybe a nutritional deficiency could decrease eosinophils or basophils or any other white blood cell for that matter. Also, excessive exposure to glucocorticoids could do it. But again, a little bit tricky, okay?
Okay, let's move on. Now on to the last one of the polymorphonuclear cells or the granulocytes, and those are the basophils. Basophils are named basophils because of the way they take up basic dyes, in this case, giving the cell a very blue color. If you see a basophil under the microscope, it is going to look a lot like a mast cell, but the function is gonna be a little bit different.
Basophils participate in our allergic response and give us some of the symptoms that we experience with an allergic reaction. So what might be a cause of basophilia? Allergies, yes.
Also, chronic myelogenous leukemia. or some of the blood cancers, lycogicin's disease, and also oral contraceptive pills. All right, so what about basopenia next? Well, again, I mentioned this for the eosinophils. A little bit difficult to measure a decrease when the lower limit of normal is zero.
But I suppose if someone twists your arm and you have to give an answer, you could say... a nutritional deficiency, or excessive glucocorticoid use. All right, moving on. Now on to monocytes. Monocytes are the largest of all the white blood cells.
That makes them a little bit easier to pick out on a microscope slide. They can approach three times the diameter of a red blood cell. So a lot like neutrophils, monocytes are very useful little cells. However, unlike neutrophils, monocytes play more of a role in the chronic inflammation or infection vice the neutrophils, which are more of an acute phase cell. Almost half of them are stored in our spleen and are released when an infection is sensed.
They are very motile, so they are able to get themselves into the tissue where the inflammation or infection is. They have three important jobs. They phagocytose bacteria or foreign bodies and digest it.
and then they are involved in the presentation of that antigen to T cells to help the T cells do their job. And lastly, monocytes also produce cytokines, which recruit other white blood cells and also mediate the fight against the invading bacteria or against the cause of the inflammation. So given that information, a cause of monocytosis, which means an elevated level of monocytes, might be a chronic inflammatory state. Monocytes do ramp up during a stress response. You would also see a lot of them in Cushing's syndrome, some viral syndromes, and sarcoidosis.
How about monocytopenia? Well, they would be decreased in aplastic anemia, of course, because many cell lines would be decreased in aplastic anemia. AML, acute myeloid leukemia, excessive glucocorticoid use would decrease them, and some myelotoxic drugs would also decrease them. Okay, moving on. Okay, next on to lymphocytes.
There are three main types of lymphocytes. T-cells, B-cells, and natural killer cells. First up on the list are T-cells. There are three main subtypes of T cells. Helper T cells, cytotoxic T cells, and memory T cells.
Basically, the helper T cells do what they sound like they do. They help other cells in the immune system function and mature and do their job. And they do this by the production of certain cytokines.
Now, this isn't a histology lecture, so I'm not going to get into more details. Next up, the cytotoxic T cells are used... to help destroy infected cells. Now those are our own body cells that are infected with viruses.
And lastly, memory T cells, which hang around for a long time and have the ability to remember antigens so that they can react faster the next time we're infected with that same pathogen. Okay, next are B cells. And there's two main types of B cells that I want to talk about, the plasma B cells, which produce large amounts of antibodies like little factories to help us fight infections. And again, memory B cells, which hang around for a long time, just like the T memory cells.
And they have the ability, a lot like the memory T cells, to remember the antigens of specific infections to help speed up our response the next time we're infected with that pathogen. And lastly, natural killer cells. They are not the same as cytotoxic T cells, but they play a similar role by helping us to kill infected cells or cancer cells. So that being said, what could be a cause of lymphocytosis?
How about viral infections? Perfect, right? Do you remember which kind of white blood cells respond initially to a bacterial infection?
Well, that would be neutrophils. Lymphocytes are more geared toward protecting us against viral infections. So in a viral infection, you would expect that to go up. What else?
Leukemias. This is pretty obvious, right? There's pretty much a reason for an increased number of most or all of the previous white blood cells we've talked about.
And adrenal insufficiency. can be a cause of lymphocytosis. What about lymphocytopenia? Well, here's a good one. HIV.
This virus destroys T cells, specifically the CD4 T cells. So this could be an early indicator, along with a physical exam and a history, that could point you towards doing more specific tests for HIV in a patient. Alright, next up, aplastic anemia.
That would decrease a lot of cells. Glucocorticoid use, again. Systemic lupus erythematosus. and rheumatoid arthritis. Cool?
Let's move on. Thanks for watching, guys. Hey look, if you're trying to find the next video or part two of the CBC little mini lecture series, then just click on the link here on the screen and it will take you right to it.
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Good luck!