Med-Surg Immune System, part 4: Immune Diagnostic Tests - WBCs, Neutrophils, ESR, CRP
In this article, we cover the most important lab values and diagnostic tests for the immune system, including WBCs, neutrophils, differential WBCs, ESR, and CRP. These are the key lab values you need to learn and remember for Med-Surg and Critical Care topics in the immune system. These topics are covered in our Medical-Surgical Flashcards (Immune system), and Cathy’s video follows along with the cards.
All of these lab values are covered in our Lab Values Flashcards which make memorization easy!
White blood cells
White blood cells are a key part of the immune system that help the body fight infection and disease.
Total white blood cell count
In general, your white blood cell count should be between 5,000 and 10,000 mm³. The mm³ unit here means cells per cubic (³) millimeter (mm). A cubic millimeter is a unit of volume used for blood on diagnostic tests, also called a microliter (μl), which is about one-millionth of a liter. A drop of blood comprises about 50μl, so 1μl is about one-fiftieth of a drop of blood. That means a normal white blood cell count is at least (5000 x 50) 250,000 white blood cells per drop of blood!
A white blood cell count over 10,000/mm³ is considered leukocytosis. When you see leukocytosis, it is a strong indicator that the patient is fighting some sort of infection.
A white blood cell count under 4,000/mm³ is considered leukopenia. When you see leukopenia on a WBC test, it can be due to a number of different causes that lower WBC counts, including cancer, autoimmune disorders, certain medications, or an infection. If a patient has leukopenia, they are at a much higher risk for infection because they don’t have enough white blood cells to fight off the infection.
Differential white blood cell count
A differential white blood cell count is a test that a provider might order for your patient when they are trying to determine the type of infection the patient has. This test differentiates between the different types of white blood cells, showing the relative percentage of each. There are five main types of white blood cells, and they make up standard portions of the blood. But, specific types of WBCs can be elevated for specific types of infections.
It may be helpful to think of this test like a pie chart. If there is one type of WBC that normally takes up ⅓ of the chart, but suddenly it’s taking up ½ of the chart, you know the presence of that WBC type has increased, and that can be the clue to determine what type of infection the patient may have.
Types of white blood cells
The five types of white blood cells are as follows:
In the table below, we outline the normal ranges for the different types of white blood cells.
|White blood cell type||Normal Range||Reason for Increase|
|Neutrophils||55-75% of WBCs (can vary by lab)||Acute bacterial infection|
|Lymphocytes||20-40% of WBCs||Chronic bacterial infection, viral infection, leukemia, lymphoma|
|Monocytes||2-8% of WBCs||Protozoal or viral infections, tuberculosis, chronic inflammation|
|Eosinophils||1-4% of WBCs||Allergic reactions, parasite infections|
|Basophils||0.5-1% of WBCs||Allergic reactions (basophils release histamine), leukemia|
With basophils you might need benadryl!
Neutrophils make up the largest percentage of white blood cells in the body, between 55-75% of white blood cells. This range can vary between facilities and laboratories, but the approximate normal range for neutrophils is between 2,500 - 8,000/mm³.
A patient with a neutrophil count under 2,000/mm³ has neutropenia, which means they are at very high risk for infection.
Neutrophils are produced by the bone marrow and can increase when a patient is fighting an acute bacterial infection. It may be helpful to think of neutrophils as the first responders of the white blood cells. They are the first to arrive to help fight a virus or bacteria.
Neutrophils are the first to neutralize the threat.
Left shift/”banded” neutrophils
One important concept about neutrophils you’ll likely need to know for your exams is banded neutrophils, or what’s known as a left shift. Normally, the bone marrow produces neutrophils and releases them into the body to help fight infection. If the body is fighting an overwhelming infection, the bone marrow cannot keep pace, and needs to start releasing immature, non-fully functional neutrophils out into the body.
This would be akin to a country fighting a war, sending all their adult soldiers out, but still being overwhelmed on the battlefield. So the country has to send teenagers and kids out to the battlefield to try to continue to fight.
Erythrocyte sedimentation rate (ESR)
Another lab value that’s important to know for the immune system is a patient’s ESR levels. ESR is a measure of how quickly red blood cells settle at the bottom of a test tube. Usually, these red blood cells settle slowly. The expected range is under 20 mm/hr.
Increased ESR levels are any amount over 20 mm/hr, and indicate the presence of inflammation due to infections, tumors, or autoimmune diseases like rheumatoid arthritis. Levels 20-40 mm/hr indicate mild inflammation, 40-70 mm/hr indicates moderate inflammation, and ESR levels over 70 mm/hr indicate severe inflammation.
C-reactive protein (CRP)
C-reactive protein (CRP) is another lab value that’s important to know for the immune system and is an indicator of inflammation. CRP is a protein made by the liver that is released into the bloodstream during inflammation (reactive to inflammation). The expected range for CRP is less than 3.0 mg/dL.
CRP levels over 3.0 mg/dL indicate the presence of inflammation due to infection or the flare-up of chronic inflammatory conditions like rheumatoid arthritis, lupus, or IBD.
CRP has 3 letters, and normal levels are under 3.
If you need an easy way to memorize WBCs, ESR, and CRP levels, check out our Lab Values Flashcards. Cathy’s teaching on the immune system is intended to help prepare you for Medical-Surgical nursing exams. The Medical-Surgical Nursing video series is intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI and NCLEX.
Alright! In this video, I am going to go over some diagnostic tests that are associated with the immune system. If you're following on cards, I am on card number 10.
We're first going to talk about white blood cells.
So your white blood cell count should be between 5,000 and 10,000. That's what the normal range is.
If your patient has a white blood cell count over 10,000, that is considered leukocytosis, and that is a strong indicator that the patient is fighting some sort of infection.
If the patient has a white blood cell count under 4,000, then that is considered leukopenia.
And if a patient has leukopenia, that could be due to a number of causes which include cancer, an autoimmune disorder, or certain medications or infections can cause a drop in the number of white blood cells.
But if your patient has leukopenia, then they are at high risk for infection because they have insufficient white blood cells to help fight off those infections.
Alright. Let's talk about neutrophils.
Neutrophil count should be between 2,500 and 8,000.
If we have neutrophils under 2,000, that is considered neutropenia.
We may also have something called banded neutrophils or a left shift. And that's an important thing to know what that means. So normally, the bone marrow is producing these neutrophils and releasing them out into the body to help fight infection. If the body is fighting an overwhelming infection, that bone marrow cannot keep pace, right? They are producing all the neutrophils they can, but it's not enough to fight this overwhelming infection. So they start releasing immature neutrophils out into the body.
It would be like if we're fighting a war, if our country's fighting a war, and we've sent all our adult soldiers and they're still not getting the job done. It's a really bad war. We start sending our kids and our teenagers and 13-year-olds, immature soldiers out there to try to fight that war. It's kind of like the same thing that the bone marrow's doing. If the infection is so bad that the mature neutrophils that they've released into the body aren't getting the job done, they'll start sending out immature neutrophils before they are fully functional. So again, that is considered a "left shift" or banded neutrophils.
Okay. Let's now talk about ESR. So ESR stands for erythrocyte sedimentation rate.
And if a patient has elevated levels of ESR-- so normal levels will be under 20.
If they have levels above 20, then that is a strong indicator of the presence of inflammation in the body.
In addition, CRP, which is C-reactive protein that's another indicator of inflammation.
Normal levels of CRP are below three.
If your patient has a value above three, then that is also an indicator that they have some kind of inflammation in the body. The way I remember CRP is it has three letters, right, CRP, and so that helps me to remember that normal levels are under three.
Another test that your provider may order for your patient is something called a differential white blood cell count.
So if the provider is trying to figure out what type of infection the patient may have, if they have cancer or some kind of autoimmune disorder, this test can be helpful.
There are five main types of white blood cells that are present, and this count will tell us how much is present of each kind.
So with neutrophils, neutrophils make up the largest percentage of white blood cells in the body, typically between 55 and 75% of the white blood cells.
We may have elevated levels of neutrophils when a patient is fighting an acute bacterial infection. So neutrophils are like the first responders of the white blood cells. They are the first to arrive on-site to help fight a virus or bacteria. So our little hint to remember that is that neutrophils are first to neutralize the threat.
Okay, then we have lymphocytes. Lymphocytes make up between 20 and 40% of the white blood cells, and they may be increased when a patient has a bacterial infection, a viral infection.
They can also be increased with leukemia and lymphoma as well.
Then we have monocytes. So monocytes make up about 2 to 8% of the white blood cell count.
They may be elevated with bacterial infections as well as tuberculosis.
Then we have eosinophils, which make up just 1 to 4% of the white blood cells.
They are elevated with allergic reactions as well as parasite infections.
And then finally we have basophils. Basophils make up just 0.5 to 1% of the white blood cells. They are elevated during allergic reactions. So basophils will release histamine when you're having an allergic reaction, and with that histamine, you may need to take an antihistamine, such as Benadryl, to help cope with the symptoms of all that histamine.
So the little saying we have here to help you remember that is that with basophils, you might need Benadryl, because those basophils release that histamine and Benadryl is an antihistamine to help you with those symptoms. And hopefully it will help you remember that with basophils, you're thinking allergic reaction.
So that is it for the differential white blood cell count. When I come back for my next video, we will start getting into disorders, starting with Lupus. Thank you so much for watching.
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