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Monocyte Disorders


Mary Territo

, MD, David Geffen School of Medicine at UCLA

Last full review/revision Aug 2021| Content last modified Aug 2021
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Monocytes are a type of white blood cell Overview of White Blood Cell Disorders White blood cells (leukocytes) are an important part of the body’s defense against infectious organisms and foreign substances (the immune system). To defend the body adequately, a sufficient... read more Overview of White Blood Cell Disorders that fight certain infections and help other white blood cells remove dead or damaged tissues, destroy cancer cells, and regulate immunity against foreign substances.

Monocytes are produced in the bone marrow and then enter the blood, where they account for about 1 to 10% of the circulating white blood cells (200 to 600 monocytes per microliter of blood [0.2 to 0.6 × 109 per liter]). After a few hours in the blood, monocytes migrate to tissues (such as spleen, liver, lungs, and bone marrow tissue), where they mature into macrophages.

Low or high numbers of monocytes do not usually cause symptoms. However, people may have symptoms of the disorder that caused the change in monocyte number.

Diagnosis is by blood testing (complete blood count) done when a person has signs or symptoms of an infection or autoimmune disorder. Sometimes the condition is discovered by chance when a complete blood count is done during a routine physical or for the evaluation of another condition.

Treatment for monocyte disorders depends on the cause.

Increased number of monocytes

An increased number of monocytes in the blood (monocytosis) occurs in response to chronic infections, in autoimmune disorders, in blood disorders, and in certain cancers. An increase in the number of macrophages in parts of the body other than in the blood (such as the lungs, skin, and other organs) can occur in response to infections, sarcoidosis Sarcoidosis Sarcoidosis is a disease in which abnormal collections of inflammatory cells (granulomas) form in many organs of the body. Sarcoidosis usually develops in people aged 20 to 40, most often people... read more Sarcoidosis , and Langerhans cell histiocytosis Pulmonary Langerhans Cell Histiocytosis Pulmonary Langerhans cell histiocytosis is a disorder in which cells called histiocytes and eosinophils (types of white blood cells) proliferate in the lungs, often causing scarring. People... read more .

Low number of monocytes

MonoMAC syndrome

Symptoms vary depending on the specific microorganism that causes the infection but often involve the lungs or skin.

Diagnosis is by a blood test that shows the absence of monocytes and by genetic testing.

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