What is Leukocytosis? - Causes & Types

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  • 1:35 Leukocytosis & Causes
  • 2:43 Types
  • 6:14 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Leukocytosis is an increased number of white blood cells. It is often an indication of infection. Learn about the causes of leukocytosis and the five types: neutrophilia, lymphocytosis, monocytosis, eosinophilia and basophilia.

White Blood Cells (Leukocytes)

In this lesson, we will be focusing on a type of cell in your body called white blood cells. A good way to think of white blood cells is as soldiers that defend your body against infection and disease. Now, just like there are different types of soldiers in the military, such as Navy officers, Army sergeants, and Air Force airmen, there are different types of white blood cells in your body. In fact, there are five different types of white cells. The most numerous are neutrophils, and then we have lymphocytes, monocytes, eosinophils and basophils. These white cells have different jobs, just like soldiers, but in the end, they are all working together to defend the body. In this lesson, we will learn more about these white blood cells and what can cause them to increase in number.

Now, we mentioned the five types of white blood cells. I like to use a mnemonic to remember their names and their order from greatest concentration in the body to least. The mnemonic is 'Never Let Mamma Eat Beans,' which stands for neutrophils, lymphocytes, monocytes, eosinophils and basophils. We will look more closely at these different cells in just a minute, but for now, we can think of them collectively as white blood cells or leukocytes, which is their more formal name. The term 'leukocytes' comes from the Greek language. 'Leuko' is the Greek word for 'white' and 'cytes' means 'cells.'

Leukocytosis and Causes

When leukocytes or white blood cells increase in number, we have a condition called leukocytosis. This term is easy to recall if you remember that in pathology it's common to put the suffix '-osis' on the end of a word to signify that it is a condition. So we put '-osis' on the end of 'leukocyte' to indicate that we have a problem with the white blood cells.

Now that we know the term, we have to ask, what are the causes of leukocytosis? Well, let's think about this. The white blood cells are soldiers, and their main job is to fight off infection. So if you have a lot of white blood cells being called into active duty, it's a pretty good indication of infection. Therefore, leukocytosis is often caused by an infection. This could include many infectious disorders, like tuberculosis or pertussis, which is commonly known as whooping cough. But leukocytosis is not limited to infection. It can also be caused by certain cancers and inflammatory conditions.

Types of Leukocytosis

Because there are five types of leukocytes, it makes sense that any of these cells could increase in number. Therefore, we see that there are five types of leukocytosis. Let's look at these different types from the most abundant leukocytes to the least abundant.


You recall from our 'Never Let Mamma Eat Beans' mnemonic that the first cell we mention is neutrophils. If there is an increase in neutrophils, we have the first type of leukocytosis, which is neutrophilia. The suffix 'philia' means 'love.' So you can think of neutrophilia as the body loving neutrophils so much that it makes more of them. Because this is the most numerous leukocyte, it's going to be the primary soldier and fight off many things, but the main cause of neutrophilia is bacterial infection. This makes sense because neutrophils are particularly well-equipped to neutralize bacterial infections. If bacteria are infecting the body, there is a good possibility that neutrophils are on the front lines acting to 'neutralize' the enemy.


The next type of leukocytosis that we see is lymphocytosis. This is, as you might guess, an increase in lymphocytes. And did you notice that when the white blood cell ends in the suffix '-cyte,' the condition simply adds an additional suffix, '-osis'? This is different than the cells that end in '-phil,' like neutrophil. For those conditions, we change 'phil' into 'philia.' So 'neutrophils' become 'neutrophilia' and 'lymphocytes' become 'lymphocytosis.'

For 'lymphocytosis,' you might want to underline the word 'lymph' because lymphocytes are white blood cells that can be found in lymph organs, such as the lymph nodes and spleen.

If you have a swollen lymph node, the first thing you think about is infection. So we see that lymphocytosis is caused by infection. But swollen lymph nodes can also be seen in certain cancers of the lymphatic system. So if lymphocytosis is present, this would need to be ruled out.

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