Basophils: What High and Low Levels Mean

A basophil is a type of white blood cell that is a part of your immune system. They make up only around 1% or less of all white blood cells but are among the largest. The cells not only provide frontline defense against infection but are also involved in processes like inflammation and allergies.

This article details the structure and function of basophils as well as the diseases and conditions associated with high or low basophils.

What Do Basophils Do?

Basophils are a type of white blood cell, or leukocyte. White blood cells play a role in the body's immune defense and protect the body against infectious diseases and foreign invaders.

Basophils are part of the innate immune system. This is the immunity you are born with as opposed to immunity you later develop after infection or vaccination.

As part of the innate immune system, basophils do not make you immune to an infection you have had in the past. They are simply among the frontline cells that attack any foreign agent that enters the body.

Basophils are most effective in protecting against bacteria and parasites, including parasites like ticks and worms.

How Basophils Work

Basophils help trigger inflammatory reactions. Inflammation is the body's natural response to anything that might cause it harm. It is the body's way of signaling the immune system to heal and repair damaged tissues as well as defend itself against foreign agents.

The granules inside the basophils contain histamine and heparin, among other things. Each has a different role:

• Histamine is a vasodilator, meaning that it causes blood vessels to widen. This brings more immune cells to the site of an injury or infection.
• Heparin is an anticoagulant (blood thinner). It is produced by the body to prevent blood clots from forming at the site of an injury or infection.

Basophils also indirectly attack foreign agents by binding to a type of white blood cell called B-cell lymphocytes. The binding causes B-cells to release antibodies called immunoglobulin E (IgE) into the bloodstream. IgE has strong action against parasites and venoms.

What Is a Normal Basophil Count?

The composition of white blood cells is measured with a test called a white blood cell (WBC) count, of which basophils account for between 0.5% to 1%. The actual number of basophils is measured with a test called the absolute basophils count (ABC) described in cubic millimeters (mm3).

A normal ABC is between 15 and 50 mm3. When the count is outside of this range, it is considered abnormal.

Abnormal Basophil Counts

An abnormal basophil count is described as either basophilia (high basophils) or basopenia (low basophils):

• Basophilia occurs with an ABC over 50 mm³.
• Basopenia occurs with an ABC under 15 mm³.

It is common for basophil levels to be outside normal range and it doesn't always signal a serious condition, though in some cases it might. A healthcare provider can help determine the cause of your abnormal basophil levels by reviewing your symptoms and giving you a physical exam. They may order further tests to help identify the source of the abnormal count.

What Causes High Basophils?

There are a number of conditions that can cause your basophil counts to be higher than normal.

Chronic Inflammation

Conditions that cause chronic inflammation are associated with basophilia. Infections such as influenza or tuberculosis can cause basophilia, as can certain autoimmune diseases. They include:

• Inflammatory bowel disease (IBD)
• Rheumatoid arthritis
• Psoriasis

Allergies

An allergy is an abnormal response by the immune system to a substance or event that is otherwise harmless. The histamine released by basophils is one of the main causes of allergy symptoms. When the body is exposed to an allergen (allergy-causing substance), basophils and related cells called mast cells will break open.

The release of histamine causes blood vessels to widen, which causes fluid to leak into surrounding tissues. This can lead to redness and swelling of the skin in the form of rash, hives, or angioedema (swelling under the skin). It can also cause nasal symptoms and breathing problems as those tissues swell and become inflamed.

Histamine is also involved in itching. It does so by attaching to proteins called H1 receptors in the skin, triggering abnormal sensations in surrounding nerve fibers.

Hypothyroidism

When you have hypothyroidism, your body doesn't produce enough thyroid hormone. This can cause bodily functions to slow down, leading to basophilia.

Leukemia and Lymphoma

Basophilia can also be a feature of certain types of cancers, such as leukemia and lymphoma. Accelerated chronic myeloid leukemia (CML) is often marked by very high basophil levels of 20% or more. People with Hodgkin's lymphoma may also have elevated basophils.

What Causes Low Basophils?

Several factors can cause basopinia.

Acute infections

Acute infections such as the common cold or a kidney infection can also cause basophil levels to be too low if the infection is taking a longer than normal time to heal. This is the result of basophils working overtime to try to attack the virus.

Severe allergies

Severe allergic reactions, such as hives, can cause basopinia. Allergies are the result of your body overreacting to a foreign substance.

Hyperthyroidism

Hyperthyroidism is a condition where your body produces too much thyroid hormone. This causes your bodily processes to speed up, which may cause basophils to work too hard.

Certain Medications and Treatments

Prolonged steroid use can cause low basophil levels, as can certain treatments, such as radiation and chemotherapy. These treatments disrupt the production of basophils and can therefore make counts lower than normal.

Summary

Basophils are a type of white blood cell called a granulocyte. As part of the innate immune system, basophils are one of the frontline defenders against diseases, including parasites.

High basophils (basophilia) may be caused by infections, autoimmune diseases, and cancer, while low basophils (basopenia) may be caused by acute infection, hives, medications, and cancer treatments. Basophils also play a role in allergies by releasing an allergy-causing chemical called histamine into the bloodstream.