What Is It, Common Causes, Treatments and More

Author: Alyssa Haag

Editors: Ahaana Singh, Lisa Miklush, PhD, RN, CNS

Illustrator: Aileen Lin

What is granulocytosis?

Granulocytosis occurs when an individual has too many granulocytes, which are a category of white blood cells in the blood. Granulocytes are characterized by the presence of granules, or small particles, that improve their function. They can be further classified as mast cells, neutrophils, eosinophils, and basophils. When referring to granulocytosis, however, it is usually related to an increase in neutrophils, eosinophils, or basophils.

What is the function of granulocytes?

Granulocytes assist the immune system in fighting off foreign invaders—such as viruses, bacteria, parasites, and fungi—that cause infection or inflammation. Neutrophils play a major role in fighting off bacterial infections; eosinophils play a major role in fighting off parasites; and basophils and mast cells play a major role in allergic reactions. Granulocytes develop in the bone marrow, which is the spongy-like substance inside bone, and after entering the blood, they respond to signals sent from the immune system. When they come in contact with foreign substances invading the body, granulocytes undergo degranulation, in which they secrete their specific granules in an effort to fight off the invaders.

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What causes granulocytosis?

Granulocytosis may be caused by bone marrow disorders, and may also be seen in conjunction with infections and autoimmune disorders. 

Most commonly, granulocytosis is caused by bone marrow disorders which cause the number of granulocytes produced in the marrow to increase. One of the most common bone marrow disorders resulting in granulocytosis is chronic myeloid leukemia, a cancer of the white blood cells. Other bone-marrow-related disorders that can result in granulocytosis include polycythemia vera (causing an increase in red blood cells), primary myelofibrosis (causing destruction of the bone marrow and consequent bone marrow scarring), and essential thrombocythemia (causing an increase in platelets). 

Infections, especially those caused by bacteria, can also cause granulocytosis. Such cases result from the body’s natural immune response to fight off the infection; as more neutrophils are produced in order to attack the bacteria, granulocytosis may occur.

Finally, autoimmune disorders, such as rheumatoid arthritis may also result in granulocytosis. Individuals with rheumatoid arthritis generally have chronic inflammation of the joints which can often result in an increased amount of circulating granulocytes.

What are the signs and symptoms of granulocytosis?

The signs and symptoms of granulocytosis depend on the underlying cause. If it is the result of chronic myeloid leukemia, common signs and symptoms include abnormal bleeding, fatigue, loss of appetite, pale skin, night sweats, and frequent infections. In cases of rheumatoid arthritis-related granulocytosis, common signs and symptoms include joint pain, swelling, and stiffness. If it is related to a bacterial infection, common signs and symptoms include fever, fatigue, headache, nausea, and vomiting.

How do you diagnose granulocytosis?

Most often, granulocytosis is diagnosed by a blood test called a complete blood count (CBC). A CBC measures the amount of red blood cells, white blood cells, and platelets in an individual’s blood. Elevated white blood cell counts can indicate granulocytosis as well as an underlying disorder, disease, or infection. Similarly, elevated red blood cells or platelets can be indicative of polycythemia vera or essential thrombocythemia, respectively.

How do you treat granulocytosis?

Treatment for granulocytosis is usually targeted at treating the underlying cause. Treating the existing condition should assist in decreasing the number of white blood cells in the blood and resolve the granulocytosis.

What are the most important facts to know about granulocytosis?

Granulocytosis occurs when there is an increase in the number of granulocytes (e.g. neutrophils, basophils, or eosinophils) in the blood. Granulocytosis is usually a symptom of an underlying condition or disease, specifically bacterial infections, autoimmune disorders or bone marrow disorders. Diagnosis involves a complete blood count and treatment is targeted at mediating the underlying cause.

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Related links

Chronic leukemia
Introduction to the immune system
Nonbenzodiazepine anticonvulsants
Polycythemia vera

Resources for research and reference

Blood Components. (n.d.). In American Red Cross. Retrieved, November 24, 2020, from

Chronic myelogenous leukemia. (2019). In Mayo Clinic. Retrieved November 24, from