Health & Medicine Medical Tests

Basophils: Definition, Function, and Normal Range


The human body has built-in abilities to fight foreign organisms, called the immune system. White blood cells (WBCs) form the principal component of the immune system. These have the capability to identify and fight invaders. The WBCs are produced in the bone marrow and can be found circulating in the blood or stationed in lymph nodes.

Types of White blood cells:

There are two main lineages of WBCs:

  1. Granulocytes– these cells contain protein granules that have specific functions and according to the type of protein, they pick up different stains on microscopy. These are further divided into basophils, eosinophils, and neutrophils.
  2. Agranulocytes- these include lymphocytes and monocytes; these are the fighter cells that recognize invaders, produce antibodies, and fight off all sorts of new and old infections. These do not contain granules. 


Basophils are the white cells found in the least number in blood. As stated above, basophils are a granulocytic type of white blood cells. Their protein granules contain different but significant compounds, two of which are histamine and heparin.

How Basophils work?

When the body is attacked by allergens, basophils help block and destroy these allergens. During this process, basophils get damaged and release the histamine granules that cause allergic reactions. This is observed as itching, redness, swelling, and warmth in the reactive area. If the allergens are in high concentrations or the white cell response is severe, the allergic reaction can involve the whole body.

The second type of granules in the basophils contain heparin. Heparin is a natural blood thinner that prevents clotting and keeps the blood flowing through the body.

Basophils also attract other cells to cause allergy through a mediator called immunoglobulin E. Sometimes this mediator is measured in the blood to see the level of allergic sensitivity.

Blood range:

A total white cell count is usually done to find the accurate number of each type of white cell in a blood sample.

Normally, basophils make up the least number of white cells in the blood; 0.5-1% of all white blood cells. Their number goes up and down in response to invaders or long term diseases. 

Despite the low numbers, these are identified on routine blood cell count tests easily due to the presence of readily staining granules. But once these granules have been released, it leaves the cells shrunken and empty, which can be difficult to pick up on the regular testing.

Some doctors also check the basophil levels to see the functionality of the immune system and to diagnose certain medical conditions.


High Basophil count:

Basophilia or a high blood basophil count is seen in conditions such as

  • Allergies
  • Asthma
  • Autoimmune conditions – rheumatoid arthritis, lupus, inflammatory bowel diseases (Crohn’s disease and ulcerative colitis), diabetes, Hypothyroidism
  • Viral infection like chickenpox
  • Collagen vascular disease
  • Blood and bone marrow disorders (myeloproliferative disorders) – myelofibrosis, essential thrombocythemia, polycythemia vera
  • Blood cancers- lymphoma, leukemia
  • After removal of the spleen

Low Basophil count:

If the basophil count falls below the normal range, then it’s called basopenia. This may occur in 

  • Allergies or anaphylaxis
  • Hyperthyroidism
  • Infections 
  • Cancer
  • Severe trauma


Basophils are a vital part of the immune system and have the capability to exhibit that the body is fighting invaders.

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