What are granulocytes in a blood test

Definition

Granulocytes are a type of white blood cell that has small granules. These granules contain proteins. The specific types of granulocytes are neutrophils, eosinophils, and basophils.

Granulocytes, specifically neutrophils, help the body fight bacterial infections. The number of granulocytes in the body usually increases when there is a serious infection. People with a lower number of granulocytes are more likely to develop bad infections more often.

Granulocytes are counted as part of a white blood cell differential test.

References

Hall JE. Resistance of the body to infection: I. leukocytes, granulocytes, the monocyte-macrophage system, and inflammation. In: Hall JE, ed. Guyton and Hall Textbook of Medical Physiology. 13th ed. Philadelphia, PA: Elsevier; 2016:chap 34.

Review Date: 01/19/2019

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High immature granulocyte levels can indicate a problem with your bone marrow. It is also a sign of infection, allergic reactions, and inflammation from an underlying health condition. However, immature granulocyte high levels are also normal during pregnancy and in newborns.

Granulocytes are white blood cells. They play an important role in your immune system responding to infections and allergens. Granulocytes are typically evaluated as part of a complete blood count (CBC) blood test.

This article explains granulocytes, different types of immune cells, and what it means when immature granulocytes are high.

What Are Granulocytes?

Granulocytes are a family of specialized white blood cells—neutrophils, basophils, and eosinophils—that are produced in the bone marrow. High granulocyte levels—also known as granulocytosis—occur when there are elevated levels of these cells in the bloodstream.

Granulocyte levels are evaluated using blood work and laboratory tests such as a complete blood count (CBC). If your granulocyte levels are high, this may be an indicator of one of several processes including:

• Infection (bacterial, fungal, or viral)
• Allergic reaction
• Asthmatic reaction
• Inflammation
• Blood cancers such as chronic myelogenous leukemia
• Myelofibrosis (rare bone cancer that interferes with normal blood cell production)
  

What Are the Functions of Granulocytes?

Granulocytes are white blood cells that play a critical role in managing the immune system. They are the first cells to respond to an infection and can play a critical role in mediating allergies.

Each granulocyte has a specialized function within the body. This includes:

• Neutrophils: These are responsible for the initial response and line of defense against infection. Neutrophils respond to sources of infection within the body. They also can move and localize to a site of infection and eliminate bacteria, viruses, fungi, and parasites causing harm. Neutrophils are the most abundant cell identified at the site of infection and make up the majority of a person’s granulocyte level. Neutrophil levels can be specifically counted and are tracked during the course of an infection.
• Basophils: These help with responding to allergies and inflammation within the body. They play a critical role in recruiting other immune cells to the source of an allergy. Basophils cause inflammation through the release of histamine molecules and other chemical messengers that signal immune cells to respond. In response to an allergen, the basophil may cause an overactive immune response that can be life-threatening known as anaphylaxis. Basophil levels can also be abnormally elevated in a condition known as chronic myeloid leukemia. 
• Eosinophils: Eosinophils are responsible for managing chronic inflammation and parasitic infections within the body. They can be involved in the response of the body to allergies, cancer, and parasitic infections. Eosinophils are one of the primary cells involved in removing parasites from the body.

What Do High Granulocyte Levels Indicate?

Granulocyte levels are often high when the immune system is activated.

The immune system can be activated to fight infections that are:

• Viral
• Bacterial
• Fungal
• Parasitic

In addition, since granulocytes are involved in allergic reactions, they can be elevated in the presence of an allergic reaction to:

• A medication
• Bee sting
• Another substance

Also, since the bone marrow is where granulocytes are produced, if there is cancer in the bone marrow—such as with chronic myelogenous leukemia—then granulocyte levels may be abnormally elevated.

Other conditions that can cause elevated levels of granulocytes include:

• Polycythemia vera
• Primary myelofibrosis 
  

Treatments for High Granulocytes

There are many treatments available for high granulocyte levels.

Identifying the appropriate treatment depends on identifying the cause of the rise in granulocytes. For example:

• Infections may be treated with antibiotics.
• Allergic reactions may be treated with allergy medications and steroids.
• Cancer may be treated with chemotherapy, radiation, and bone marrow transplants.

Summary

 A high level of granulocytes in the blood is called granulocytosis. Granulocytosis is important because it can indicate an infection, autoimmune disease, or blood cell cancer.

There are many treatment options available for elevated granulocyte levels, and the treatments used depend on the underlying cause.

A Word From Verywell

A high granulocyte level may be one of the earliest signs of illness. It is normal to feel confused by the many causes of high granulocytes. More specific tests can be used to evaluate and determine the specific cause, and your healthcare provider can then recommend appropriate treatments. 

Frequently Asked Questions

• What is the most abundant granulocyte?

  Neutrophils usually account for 50%–70% of the granulocytes in the body. Levels of neutrophils, basophils, and eosinophils vary from person to person, but levels can be evaluated through laboratory tests. 
  

• What causes granulocytosis?

  The most common causes of elevated granulocyte levels, or granulocytosis, are infections, allergic reactions, and white blood cell disorders, such as chronic myeloid leukemia (CML) or myelofibrosis. 
  

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

1. MedlinePlus. Granulocytes.

2. Abdel-Azim H, Sun W, Wu L. Strategies to generate functionally normal neutrophils to reduce infection and infection-related mortality in cancer chemotherapy. Pharmacology & Therapeutics. 2019;204:107403. doi:10.1016/j.pharmthera.2019.107403

3. Karasuyama H, Obata K, Wada T, Tsujimura Y, Mukai K. Newly appreciated roles for basophils in allergy and protective immunity: Newly recognized roles of basophils. Allergy. 2011;66(9):1133-1141. doi:10.1111/j.1398-9995.2011.02613.x

4. Kita H. Eosinophils: multifaceted biological properties and roles in health and disease: Immunobiology of eosinophils. Immunological Reviews. 2011;242(1):161-177. doi:10.1111/j.1600-065X.2011.01026.x

5. Arber DA, Orazi A, Hasserjian R, et al. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood. 2016;127(20):2391-2405. doi:10.1182/blood-2016-03-643544

6. Tefferi A. Primary myelofibrosis: 2021 update on diagnosis, risk-stratification and management. Am J Hematol. 2021;96(1):145-162. doi:10.1002/ajh.26050

7. Tefferi A, Rumi E, Finazzi G, et al. Survival and prognosis among 1545 patients with contemporary polycythemia vera: an international study. Leukemia. 2013;27(9):1874-1881. doi:10.1038/leu.2013.163

By Kevin James Cyr
Kevin is a physician-in-training at Stanford University School of Medicine with a focus in cardiovascular disease and bioengineering. His publications have earned international awards, and his work has been featured in major media outlets such as NBC News.

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