Basophilia occurs when you have an abnormally high basophil level. This can be due to chronic inflammation or another condition that causes the production of too many white blood cells.

Basophils are a type of white blood cell. These cells are produced in your bone marrow.

White blood cells are part of your immune system. They release special enzymes to help protect your body against viruses, bacteria, and other foreign invaders.

Normally, basophils make up less than 1 percent of your circulating white blood cells. A healthy range is 0 to 3 basophils in each microliter of blood.

A low basophil level is called basopenia. It can be caused by infections, severe allergies, or an overactive thyroid gland.

An abnormally high basophil level is called basophilia. It can be a sign of chronic inflammation in your body. Or it can mean that a condition is causing too many white blood cells to be produced in your bone marrow.

Your doctor can check your levels of basophils by doing a blood test.

A few types of conditions can lead to basophilia:

  • myeloproliferative disorders — conditions that cause the bone marrow to make too many white blood cells, red blood cells, or platelets:
  • inflammation:
  • allergies:
    • food allergies
    • drug allergies
    • hay fever
    • allergic rhinitis
  • infections:
    • chickenpox
    • tuberculosis

High numbers of basophils can result in itching and other symptoms of an allergic reaction. Still other symptoms depend on what condition is causing the problem.

Symptoms of myeloproliferative disorders:

  • fatigue
  • weakness
  • headache
  • dizziness
  • shortness of breath
  • night sweats
  • fever
  • unexplained weight loss
  • easy bleeding or bruising
  • blurred vision or other vision changes
  • shortness of breath
  • numbness or tingling of the hands and feet
  • bone pain
  • belly pain or bloating

Symptoms of ulcerative colitis:

  • diarrhea
  • belly cramps
  • rectal pain or bleeding
  • weight loss
  • fatigue
  • fever

Symptoms of rheumatoid arthritis:

  • joint swelling
  • joint pain
  • stiffness
  • fatigue
  • fever
  • weight loss

Allergy symptoms:

  • sneezing
  • runny or stuffed nose
  • itchy, watery eyes
  • itching
  • wheezing
  • rash
  • hives
  • nausea or vomiting
  • diarrhea
  • trouble breathing
  • swelling of the mouth and tongue

Symptoms of infections:

  • coughing
  • fever
  • fatigue
  • chills
  • night sweats
  • headache
  • general unwell feeling
  • appetite loss or weight loss
  • rash

Your doctor might discover the high basophil numbers while doing a complete blood count (CBC) for another reason. After an abnormal CBC, your doctor may do a blood smear. A drop of your blood is spread on a slide to look for abnormal red blood cells, white blood cells, and platelets.

The tests you get next depend on which condition your doctor thinks might have caused the high basophil numbers.

Tests for the causes of basophilia can include:

  • Blood tests. Your doctor can order these tests to check for abnormal numbers of white blood cells, red blood cells, and platelets. Blood tests can also look for inflammation, or for abnormal levels of proteins and other substances in your blood. A blood test can also check for allergies.
  • Bone marrow biopsy and aspiration. Your doctor removes a sample of bone marrow from your hipbone. The sample is then tested in a lab to check whether your bone marrow is making healthy blood cells.
  • Genetic tests. These tests can look for the gene mutations that cause diseases like polycythemia vera and CML.
  • Ultrasound. This test uses sound waves to create pictures of your organs. It can show whether your spleen is enlarged. Some cancers and infections can cause an enlarged spleen.

Basophilia itself isn’t generally treated, but it may improve once the condition that caused it is treated.

Myeloproliferative disorders are treated with:

  • Chemotherapy. The medications used for this treatment destroy extra blood cells in your body.
  • Radiation therapy. This treatment uses high-energy X-rays to kill extra blood cells.
  • Surgery. If your spleen is enlarged, your doctor can remove it. This operation is called a splenectomy.
  • Stem cell transplant. This procedure replaces the stem cells in your bone marrow so they can make healthy new blood cells.

Diseases like ulcerative colitis and rheumatoid arthritis are treated with drugs that bring down inflammation and suppress the immune system.

People with allergies should try to avoid their triggers (pollen, dust, pet dander, etc.) if possible. Allergy shots can desensitize you to certain types of allergens, like weeds, mold, dust, and insect stings.

Infections caused by bacteria are treated with antibiotics.

Basophilia itself doesn’t result in complications, but the conditions that cause it can. Which complications you get depend on the disease you have, but can include:

  • an enlarged spleen
  • infections
  • pain
  • abnormal blood clotting
  • bleeding
  • increased risk for cancer

Your outlook depends on which condition caused basophilia and how it’s treated. Your doctor will work determine the best way to treat your basophilia.