Causes of a High Monocyte Count

Monocytes are a special type of white blood cell found in the body that ward off infection. Having too low or too high of a count can cause problems.

White Blood Cells There are many different types of cells throughout our bodies, and also throughout our blood. Everyone has a mixture of both red and white blood cells. A special type of white blood cell known as a monocyte is necessary in everyone’s bloodstream, as it not only has the ability to ward off infection, but can also remove damaged tissue and destroy cancer cells.

What Are Monocytes? Monocytes only comprise a small part of white blood cells, and make up 1 to 10 percent of all white blood cells found in the bloodstream. They are created in the bone marrow, and only remain in the bloodstream for several hours before they bind to tissue. Here, they transform into macrophages, which are an important part of everyone’s immune system.

High Counts and Monocyte Disorders Having too high or too low of a monocyte count is considered a monocyte disorder. There are several reasons that a monocyte count could be too high. This is a condition known as monocytosis, and is most often a response to a chronic, pervasive infection and illness. Because of the way that monocytes transform into macrophages, monocytosis also causes an increase in the number of macrophages in the body. Other reasons for an increase in monocyte count could include the presence of cancer, an autoimmune disorder or certain blood disorders.

Autoimmune Diseases There are other known causes of a high monocyte count, including the diseases sarcoidosis and Langerhans cell histiocytosis. In the disease sarcoidosis, inflammatory cells gather in areas of the body, affecting many organs (often the lungs). This disease typically strikes during the ages of 20 to 40 years old, and can present itself as a persistent cough. It is commonly diagnosed in those of Scandinavian descent, and African-Americans. Pulmonary Langerhans cell histiocytosis is a similar but different disease. Also found in the lungs, patients may experience shortness of breath or difficulty breathing because of the presence of an abundance of histiocytes and eosinophil cells in the lungs, which often causes scarring. This disease contributes to a high monocyte count as well.

Low Counts Low monocyte counts can also be a problem, and there are several causes of these as well. Low monocyte count is most often attributed to a decrease of white blood cells. Not surprisingly, because of the way chemotherapy affects patient, it is a main cause of low monocyte count. Other causes include the diseases neutropenia and lymphocytopenia. A bloodstream infection or disorder of the bone marrow can also cause a low count.

Having Tests Performed If a high (or low) monocyte count is suspected, blood tests are the best way to determine if there is an issue. The treatment depends on the monocytes count, and what the root cause is. For example, if a high or low count is caused by an autoimmune disorder, then a doctor would treat the autoimmune disorder to raise or lower the monocyte count. There is also a condition known as MonoMAC syndrome, which is a complete absence of monocytes. In this case, more extensive treatment may be needed.