Have you been told by your doctor that you have a decreased lymphocyte count? If this was discovered on a routine blood test, you may feel fine and have no symptoms at all, although you may be concerned as to why. What causes a decreased lymphocyte count on a blood test?
What Are Lymphocytes?

Lymphocytes are a type of white blood cell that’s responsible for protecting the body against bacterial and viral infections. They make up anywhere from fifteen to forty percent of the total white blood cells that circulate in the bloodstream. The two main types of lymphocytes are T cells and B cells and both help to fight off infection and play a role in stopping the growth of cancers. B cell lymphocytes are the special cells that produce infection fighting antibodies. For this reason, people with a decreased lymphocyte count may be more susceptible to certain types of infections. There is also a subtype of T cell known as a natural killer cell that helps to destroy cells infected by viruses as well as tumor cells.

How is a Low Decreased Lymphocyte Count Detected?

When a routine blood cell panel is drawn, the lab performs a differential count which shows the proportion of each type of white blood cell along with the total number of white cells present in the sample. There’s a range established for what’s normal and the values can be compared against these values. When lymphocyte counts are below fifteen percent of the total white blood cell count, it’s considered to be an abnormally low reading.

What Causes a Decrease in Lymphocytes?

One of the most common causes is an underlying viral infection. Viral infections can cause a temporary drop in lymphocytes as more of them are drawn away to fight the infection, but the lymphocyte count usually returns to normal within weeks after the infection is resolved. One of the more serious viral causes of a decrease in lymphocytes is infection with the HIV virus. In this case, a low lymphocyte count is very likely to lead to infection with “opportunistic” pathogens, ones that typically don’t cause disease in a normal person.

Another Reason for a Decrease in Lymphocytes

Lymphocytes are made in the bone marrow which means that when the bone marrow isn’t functioning properly, lymphocyte counts can drop. This can occur in a condition known as aplastic anemia. There are also certain inherited conditions where the body doesn’t make enough immune cells, resulting in a decrease in lymphocytes.

Some Drugs Can Decrease Lymphocytes

If you’ve recently taken steroids or had radiation or chemotherapy, it can cause lymphocyte counts to drop temporarily. People who undergo chemotherapy, radiation, or steroid treatment are more susceptible to infection due to their lowered lymphocyte count. Usually this all reverses upon stopping the treatment.

Other Causes of a Decreased Lymphocyte Count

Some neurological diseases such as multiple sclerosis and Guillain-Barre syndrome cause lymphocyte counts to drop, as can autoimmune problems such as rheumatoid arthritis.. Some cancers can also cause a decreased lymphocyte count, usually ones involving the blood or lymph system.

The Bottom Line

A decreased lymphocyte count may be a temporary response to a virus or can result from use of medications such as steroids. In other cases, it can indicate a more serious infection or an underlying autoimmune disease or cancer. If the lymphocyte count is only slightly below normal, your doctor may want to repeat it in a few weeks as long as you’re having no other symptoms. If it persists, you may need further tests. Be sure to follow up with your doctor if you have a decreased lymphocyte count as you may be at higher risk of infection.