Basophils are white blood cells from the bone marrow that play a role in keeping the immune system functioning correctly.

Doctors may order basophil level tests to help diagnose certain health problems. If basophil levels are low, this may be a sign of an allergic reaction or another condition. High basophil levels may indicate an autoimmune condition or one of several types of blood disorder.

In this article, learn more about the function of basophils and what abnormal basophil levels mean.

Blood tests may reveal basophil levels that are too high. The medical term for this is basophilia, and there are several possible causes:

Autoimmune inflammation

High levels of basophils may indicate rheumatoid arthritis.

High levels of basophils may indicate chronic inflammation in the body.

Immune reactions or autoimmune conditions that cause chronic inflammation include:

Hypothyroidism

High basophil levels may also be a sign of low thyroid function, or hypothyroidism. This condition occurs when the body does not produce enough thyroid hormones, which may cause some bodily functions to slow down.

Hypothyroidism can cause a variety of symptoms, including:

Some people with hypothyroidism may also notice changes in their hair or skin. The skin might become dry or rough, while the hair may turn coarse and brittle and break very easily.

Myeloproliferative disorders

Myeloproliferative disorders affect white blood cells and may also cause very high basophil levels.

Myeloproliferative disorders include:

  • Myelofibrosis: In people with this condition, fibrous tissue begins to replace the cells that make blood in the bone marrow. This disruption may lead to deformed or misshapen red blood cells and anemia.
  • Essential thrombocythemia: This condition causes the body to make too many platelets, leading to excessive blood clotting. It may also lead to circulation and nerve problems.
  • Polycythemia vera: This is a blood condition that causes the bone marrow to overproduce red blood cells.

Cancer

In very rare cases, high basophil levels may indicate certain types of blood cancer, including leukemia and lymphoma.

Basopenia is the medical term for abnormally low basophil levels.

When a basophil releases its granules in response to an invader or inflammation, it becomes empty. As an empty basophil will not show up on blood tests, the test may show a lower number of these cells.

Conditions that can cause low levels of basophils include:

Hyperthyroidism

In people with hyperthyroidism, the thyroid gland overproduces thyroid hormones, causing bodily functions to speed up.

Hyperthyroidism may cause noticeable signs and symptoms, such as:

Allergic reactions

Having an allergic reaction may cause low levels of basophils.

Low levels of basophils may be due to the body reacting to an allergen, causing the basophils to release their histamine. Other signs of an allergic reaction include:

  • puffy, red eyes
  • a runny or stuffy nose
  • excess mucus
  • hives

Severe allergic reactions may cause a potentially life-threatening situation called anaphylaxis. Signs of anaphylaxis include:

  • swelling in the face, throat, or mouth
  • difficulty breathing
  • lightheadedness
  • wheezing

Anaphylaxis can be life-threatening. Anyone having an anaphylactic reaction should seek emergency medical attention.

Infections

Basophils are instrumental to immune system function, so low levels may also signal that the body is fighting an infection.

In these cases, a doctor may recommend medications or rest until the infection clears, after which they will order blood tests to get more accurate results.