What Are Basophils?

Basophils are a type of white blood cell. White blood cells are part of your body’s immune system and help fight infection and disease. Less than 1% of your white blood cells are basophils, but even at that small portion, basophils still play an important role in your body’s immune system. 

Basophils’ main role is to respond to allergic reactions and chronic inflammation. As the cells work to fight off these conditions, their numbers can increase. Under certain conditions, it is also possible for basophils to decrease in number.

A blood test can determine your basophil count. Knowing if your basophil count is higher or lower than usual can shed light on whether you may have something like an infection or inflammation.

A healthcare worker holds up two test tubes of blood

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What Do Basophils Do?

Like all white blood cells, basophils help fight infections and other diseases. Basophils are made inside the soft portion of your bone known as bone marrow. From there, the cells migrate into your bloodstream to carry out their function. As needed, basophils also migrate into the spleen, lung, and liver.

Basophils are among the first-line defenders against foreign substances in our body. When activated, such as by an allergic reaction or asthma attack, basophils release histamine and other chemical substances.  These substances can cause symptoms like sneezing and itching in an attempt to rid the foreign substance.

Basophils also have a role in helping your body fight off parasitic infections.

Measuring Basophils

Basophils are measured as a part of the complete blood count (CBC) test with differential. A CBC is a blood test that measures several features of your blood, including the total number of white blood cells. When the CBC has differential, that means the white blood cell count will be broken down by the count of each type of white blood cell, including basophils.

To perform a CBC with differential, a healthcare provider will draw blood, usually from a vein in your arm. The small sample of blood is collected in a small tube. The blood will then be analyzed for the basophil count and the other components of the blood a CBC includes.

A CBC with differential can be a routine part of your general physical exam. A healthcare provider may also request you get a blood differential test if you have symptoms like weakness or unexplained bruising. These might be signs of a condition diagnosable with the help of a CBC with differential. The blood test can also help manage already-diagnosed conditions.

Basophil Count Results

The basophil count in the CBC is usually reported as the percentage of basophils in a certain volume of blood. The normal basophils count is usually 0-1%, though there might be slight changes in the count at different laboratories. You might also see the count measured by cubic millimeters. Typically, there are 0-100 basophils per cubic millimeter.

An abnormal basophil count is usually a sign of an underlying health condition. The number of basophils in the human body can change due to several reasons, including allergy, infection, and inflammation. Further testing and examination will likely need to be done to determine the cause.

What Does a High Basophil Count Mean?

A high basophil count is called basophilia. Basophilia can occur for several reasons, including:

  • Allergic reactions, like to venom or pollen
  • Chronic inflammation due to infections like influenza and tuberculosis
  • Chronic inflammation due to autoimmune diseases like inflammatory bowel disease
  • Blood cancers like chronic myeloid leukemia, acute myeloid leukemia, and polycythemia vera
  • Primary myelofibrosis, a blood disorder
  • Essential thrombocythemia, a bone marrow disorder
  • Certain medications
  • Certain food

Based on any signs and symptoms you may have, your healthcare provider can determine what is actually causing your basophilia.

What Does a Low Basophil Count Mean?

A low basophil count is known as basopenia. Basopenia can occur due to a variety of factors, including:

  • Certain medications, like prolonged steroid use 
  • Certain treatments, such as radiation and chemotherapy
  • Acute infections
  • Stress reactions, like in the case of pregnancy and heart attack 
  • High levels of thyroid hormone in your blood (hyperthyroidism)

Your healthcare provider can determine the cause of your basopenia based on any symptoms you may have as well as other tests.

How Are Abnormal Basophil Counts Treated?

An abnormal basophil count is usually a sign of an underlying health condition, such as an allergy, inflammation, or blood disorder. Your healthcare provider will provide you with a treatment option depending on the underlying cause.

In cases of allergic reactions, your healthcare provider may prescribe antihistamines or other medication to help manage your symptoms. If the allergy is to food, your provider will likely recommend dietary changes so that you avoid food that may trigger the allergic response.

If the abnormal count is due to a parasitic infection, your healthcare provider may prescribe medication, like Albenza (albendazole), to kill the parasite.

If blood cancer or a blood disorder is suspected, your healthcare provider may ask for further tests to reach a diagnosis. First, usually, a peripheral blood smear is done in which blood cells are looked at under a microscope. If the peripheral smear shows abnormal cells, then a bone marrow biopsy may be performed, where some bone marrow is taken out to look for different types of cells under a microscope.

If you have a basophil count that is higher or lower than usual, ask your healthcare provider about what test might be needed and how the test will help reach a diagnosis. 

A Quick Review

Basophils are a type of white blood cell that play an important role in the immune system. Present in only small amounts, these cells are produced in the bone marrow and are then released into the bloodstream. There, basophils respond to allergic reactions, asthma attacks, chronic inflammation, diseases, and infections. An abnormal basophil count—either high or low—is usually a sign of an underlying health condition. A healthcare provider will likely need to do further testing to figure out the cause of the abnormal basophil count and to determine a treatment plan.

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  1. National Cancer Institute. WBC.

  2. Min B, Brown MA, LeGros G. Understanding the roles of basophils: Breaking dawn. Immunology. 2012;135(3):192–197. doi:10.1111/j.1365-2567.2011.03530.x

  3. MedlinePlus. Basophil (close-up).

  4. Sticco KL, Pandya NK, Lynch DT. Basophilia. In: StatPearls. StatPearls Publishing; 2022.

  5. Chirumbolo S, Bjørklund G, Sboarina A, Vellad A. The role of basophils as innate immune regulatory cells in allergy and immunotherapy. 2018;14(4):815–831.doi:10.1080/21645515.2017.1417711

  6. National Cancer Institute. Basophil.

  7. MedlinePlus. Complete blood count (CBC)

  8. MedlinePlus. Blood differential.

  9. National Cancer Institute. Normal blood values

  10. Siracusa MC, Kim BS, Spergel JM, Artis D. Basophils and allergic inflammation. J Allergy Clin Immunol. 2013; 132(4):789–788. doi:10.1016/j.jaci.2013.07.046

  11. Basophil count. Nursing Critical Care. 2019;14(4):35–35. doi:10.1097/01.ccn.0000559778.07144.9d

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