What Is Lymphocytosis?

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  • Written By: Meshell Powell
  • Edited By: Melissa Wiley
  • Last Modified Date: 17 July 2018
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Lymphocytes are special types of white blood cells that form an important part of the body's immune system. The presence of an abnormally high number of lymphocytes in the blood is known medically as lymphocytosis. Although this condition can exist without the presence of disease, it is more commonly caused by factors such as infection, autoimmune disorders, or certain types of cancer. There is no specific treatment for it, as it is more of a symptom than an actual illness. Instead, the treating medical professional will likely order additional tests to find the root cause of the symptom so that the originating illness can be properly treated.

In the majority of cases, lymphocytosis is diagnosed when a medical professional is performing tests due to an illness that is already present. This symptom is rarely found by accident. The combination of various test results along with the diagnosis is often enough to help the healthcare provider to know what is causing the illness. It is possible for the lymphocyte count to be slightly elevated without any disease being present, although many medical professionals will choose to order additional tests to make sure there are no underlying health concerns.


The presence of an infection in the body is a common cause of this condition. Infections may be caused by a fungus, a virus, or bacteria. Prescription medications are often used to treat the infection, although diagnostic testing may be necessary in order to determine the source. This is an important step because treatment options for bacteria will not be useful if a virus is causing the illness, for example.

Autoimmune disorders are another potential cause of lymphocytosis. Medical conditions that compromise the immune system often cause inflammation throughout the body. This chronic inflammation may cause an elevation in lymphocytes as the body attempts to identify and battle foreign invaders. Unfortunately, when an autoimmune disorder is present, this process does not work properly, and the body ends up attacking healthy organs and tissues, leading to further problems.

Certain forms of cancer may lead to this condition as well. This symptom is most common in the types of cancer that affect the blood and the bone marrow. Cancer treatment may or may not help to resolve the elevation. Any questions or concerns about blood test results of an elevation in white blood cells should be discussed with a doctor or other medical professional.


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Post 2

@dobie - You are right that lymphocytosis is not much of a diagnosis. However, a lymphocytosis differential diagnosis can be extremely valuable in trying to place all the puzzle pieces together.

Abnormal white cell counts can tell a doctor where to look for the problem. It helps to rule out other possible causes so you narrow down the options.

We probably won't ever know everything there is to know about our immune systems. Personally, however, I think we've made great strides and the ability to interpret abnormal blood test results has no doubt saved lives.

So while lymphocytosis on its own may not tell you much, it could be the final puzzle piece that leads to a definite diagnosis. Nothing is irrelevant when it comes to the human body.

Post 1

The human body's immune system is so complex and fascinating that I find it amazing that doctors understand as much about it as they do.

I also think it can be incredibly frustrating to patients who are suffering from an undiagnosed condition to not be able to identify their lymphocytosis causes.

That's the trouble with blood tests like those that look for abnormalities in cell counts: they don't provide any conclusive data for doctors and patients, only more clues about where to look.

Don't get me wrong--I know these tests are valuable in their own right. But lympohocytosis as a diagnosis isn't much for a patient or their doctor to go on. Until we begin to understand the human immune system more, things like lymphocystosis will continue to be only pieces to the puzzle.

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