A high monocyte count can indicate the presence of a blood disorder, an autoimmune disease or a chronic infection. High monocyte levels are also linked to certain types of cancer.
Monocytes are a type of white blood cell. One of their main roles is to help the body fight off infection. Monocytes also work with other white blood cells to eliminate cancer cells, remove damaged tissue and boost the body's immunity. Monocytes mature into macrophages, which are called the scavenger cells of the immune system.
What the Numbers Mean
Monocytes are white blood cells that are related to granulocytes, which are white blood cells designed to kill bacteria. Monocytes are produced in bone marrow and then released into the bloodstream. Young monocyte cells start as monoblasts in the bone marrow. Once released, they leave the bone marrow and circulate through the bloodstream for a few hours before finding their way to other tissues, such as the spleen and lungs. Once monocytes are embedded in those tissues, they become macrophages. Macrophages support healthy immune function by destroying and ingesting pathogens. They also help lymphocyte cells recognize pathogens and create antibodies against them. Typically, there are between 200 and 600 monocytes in each microliter of blood. A number higher than 600 can indicate the presence of an underlying condition, which may necessitate additional testing. Because people may not have any other signs or symptoms, they might not be aware that they have a high monocyte count prior to going in for a blood test.
An abnormally high monocyte reading is called monocytosis. One cause of monocytosis is infection. Tuberculosis, fungal infections and endocarditis, which is a bacterial heart infection, can all raise monocyte levels. Another cause of monocytosis is a collagen vascular disease, also called an immune disorder. This family includes arthritis, scleroderma and lupus. Monocytosis can also indicate inflammatory bowel disease. It can also be a marker for certain types of cancers, including monocytic leukemia, juvenile myelomonocytic leukemia and chronic myelomonocytic leukemia.
If a routine blood test reveals an abnormal white blood cell count, doctors may prescribe a specialized test to determine which blood cells are causing the problem. This test is called a white blood cell differential. It analyzes the five types of white blood cells, which are lymphocytes, monocytes, eosinophils, basophils and neutrophils. The differential test evaluates the number of each type of white blood cell in the body and their overall numbers in relation to each other. Some diseases affect multiple types of white blood cells in addition to monocytes. Therefore, abnormal readings of other types of white blood cells can give doctors clues about the underlying condition.
A doctor will either perform the differential or complete blood test as part of a routine examination or if the patient presents with symptoms of an infection or illness, such as fever or chills, sweating and lethargy. If further testing is needed, a doctor might send a patient for a bone marrow biopsy. The physician can also use the differential test to monitor the progress of a condition or illness after it has been discovered. Treatment for monocytosis varies depending on the underlying cause.