What Are Basophils?
Medically reviewed by Isabel Casimiro, MD, PhD
Basophils are a type of white blood cell. Less than 1% of your white blood cells are basophils, but they play an essential role in your body's immune system. Basophils help your body fight infections and diseases and defend you from pathogens, allergens, and parasites.
The basophils' primary role is to respond to allergic reactions and reduce long-term inflammation. The cells respond to a threat to your health by increasing in number to help fight it. It's also possible for basophils to decrease in number.
A complete blood count (CBC) test measures and counts your blood cells, including basophils. A healthcare provider will take a blood sample and send it to a lab. A CBC test can determine whether your basophil count is too high or too low. Read on to learn what basophils are and what a high and low count means.
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What Do Basophils Do?
Basophils are among the first-line defenders against foreign substances in your body. These white blood cells trigger an inflammatory response to help fight infections and other diseases.
The cells are made inside the soft portion of your bone, or bone marrow. Basophils then migrate into your bloodstream to carry out their function. Some of the cells also migrate into the spleen, lung, and liver as needed. Basophils can also help your body fight off parasitic infections.
Basophils release histamine and other chemicals if activated. Histamine is a chemical your immune system produces to fight allergens or in response to an asthma attack. This immune response triggers symptoms like itching and sneezing in an attempt to rid your body of the foreign substance.
Basophils are essential to help fight foreign substances. It's possible for your body to mistake a harmless substance for something harmful and mistakenly trigger this immune response. This commonly occurs if you have a food allergy or seasonal allergies.
How Are Basophils Measured?
Basophils are measured as a part of the complete blood count (CBC) test with differential. A CBC measures several features of your blood, including the total number of white blood cells. A CBC with differential breaks down your white blood cell count by each type of cell, including basophils.
A healthcare provider will draw blood, usually from a vein in your arm. They will collect a small sample of blood in a tube. The blood will then be analyzed to measure the number of basophils, among other components.
Your basophil count in the CBC is usually reported as the percentage of cells in a certain volume of blood. There are typically 0–300 basophils per microliter of blood.
A normal basophils count is usually 0.5% to 1.0%. There might be slight changes in the count at different laboratories. You might also see the count measured in mm3. A normal basophil level is 0–300 basophils per microliter (μL) of blood. A count outside of this range is considered abnormal.
An abnormally elevated basophil count, or basophilia, is not always a sign of a health condition, but it can be. Basophil counts can vary depending on many factors, including allergies, infections, and inflammation. You will likely require further testing to determine the cause.
Related: What Are Lymphocytes?
What Does a High Basophil Count Mean?
A high basophil count, or basophilia, can occur for several reasons. Possible causes include:
Allergic reactions to substances (e.g., pollen or venom)
Blood cancers (e.g., chronic myeloid leukemia, acute myeloid leukemia, and polycythemia vera)
Certain foods or medications
Chronic inflammation due to the flu or tuberculosis (TB)
Chronic inflammation as a result of autoimmune disorders, such as inflammatory bowel disease (IBD)
Essential thrombocythemia, a bone marrow disorder
Primary myelofibrosis, a blood disorder
What Does a Low Basophil Count Mean?
A low basophil count is known as basopenia. Basopenia can occur due to several factors, including:
Acute infections
Certain medications (e.g., prolonged steroid use)
Certain treatments (e.g., radiation and chemotherapy)
Hyperthyroidism, or high levels of thyroid hormone in your blood
Stress reactions, like in the case of pregnancy or a heart attack
Treatment for Basophilia
An abnormal basophil count may be a sign of a health concern, such as an allergy, inflammation, or blood disorder. A healthcare provider can help you find the right treatment based on the underlying cause. Medications and surgeries, for example, can help get your basophil count back to a normal range.
Treatment for High Basophil Count
A healthcare provider may refer you to an allergist if you have allergies. An allergist may conduct an allergy test to figure out what triggers your immune system to create excess basophils. They can prescribe antihistamines or other medications to help manage symptoms. You'll likely need to make dietary changes if you have a food allergy.
A healthcare provider can refer you to an oncologist or a hematologist if they suspect blood cancer or a blood disorder. An oncologist specializes in cancer, and a hematologist specializes in blood disorders. Either specialist will likely perform further testing to reach a diagnosis.
Treatment for blood cancer depends on several factors, including the type and severity. Blood cancer treatments might include chemotherapy and radiation therapy.
Treatment for Low Basophil Count
An infection will require treatment based on what's causing it. A healthcare provider may prescribe an anti-parasite drug like Albenza (albendazole), for example, to treat a parasitic infection.
You can raise basophil counts due to hyperthyroidism by treating the overactive thyroid. Options include antithyroid medications or radioiodine therapy. A thyroidectomy, in which part of or the entire thyroid is removed, may be required.
Treatments like steroids or radiation therapy can be responsible for low basophil count. A healthcare provider might advise other treatments if possible. It's important to consult a healthcare provider about changes to your treatment plan. You never want to stop a treatment without talking to a healthcare provider first.
What To Ask Your Healthcare Provider
A healthcare provider can figure out what's causing an abnormal basophil count. Consider asking them the following if you have a count that's higher or lower than usual:
Can multiple health conditions at once cause changes in basophil counts?
How do I know what's causing a high or low basophil count?
Is there a chance there would not be an identified cause of abnormal basophil counts?
What other tests might I need? How will the tests help reach a diagnosis?
A Quick Review
Basophils are white blood cells that play a vital role in the immune system. These cells, which are in small amounts, are produced in the bone marrow and released into the bloodstream. Basophils respond to allergic reactions, asthma attacks, chronic inflammation, diseases, and infections.
An abnormal basophil count, either high or low, might be a sign of an underlying health concern. A healthcare provider can do further testing to figure out the cause and prescribe treatments.
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