What are neutrophils and what do they do?

Neutrophils are a type of white blood cell that helps heal damaged tissues and resolve infections. Neutrophil blood levels increase naturally in response to infections, injuries, and other types of stress. They may decrease in response to severe or chronic infections, drug treatments, and genetic conditions.

Neutrophils help prevent infections by blocking, disabling, digesting, or warding off invading particles and microorganisms. They also communicate with other cells to help them repair cells and mount a proper immune response.

The body produces neutrophils in the bone marrow, and they account for 55–70 percent of all white blood cells in the bloodstream. A normal overall white blood cell level in the bloodstream for an adult is somewhere between 4,500 and 11,000 per millimeters cubed (mm3).

When there is an infection or another source of inflammation in the body, special chemicals alert mature neutrophils, which then leave the bone marrow and travel through the bloodstream to the site in need.

Unlike some other cells or blood components, neutrophils can travel through junctions in the cells that line blood vessel walls and enter into tissues directly.

In this article, we look at the reasons for high or low neutrophil levels, how doctors can test these levels, and what normal neutrophil levels are for different groups.

Causes of high or low levels

There are many different reasons why a person may have higher or lower than normal levels of neutrophils in their blood.

High levels

Having an abnormally high level of neutrophils in the blood is known as neutrophilic leukocytosis, also known as neutrophilia.

Rises in neutrophil levels usually occur naturally due to infections or injuries. However, neutrophil blood levels may also increase in response to:

• some medications, such as corticosteroids, beta-2-agonists, and epinephrine
• some cancers
• physical or emotional stress
• surgery or accidents
• smoking tobacco
• pregnancy
• obesity
• genetic conditions, such as Down syndrome
• surgical removal of the spleen

Some inflammatory conditions can increase neutrophil levels, including rheumatoid arthritis, inflammatory bowel disease, hepatitis, and vasculitis.

Low levels

An abnormally low blood level of neutrophils is a condition called neutropenia.

A drop in neutrophil blood levels typically occurs when the body uses immune cells faster than it produces them or the bone marrow is not producing them correctly.

An enlarged spleen may also cause a decrease in neutrophil levels because the spleen traps and destroys neutrophils and other blood cells.

Some conditions and procedures that cause the body to use neutrophils too quickly include:

• severe or chronic bacterial infections
• allergic disorders
• certain drug treatments
• autoimmune disorders

Some specific conditions, procedures, and drugs that interfere with neutrophil production include:

• cancer
• viral infections, such as influenza
• bacteria infections, such as tuberculosis
• myelofibrosis, a disorder that involves bone marrow scarring
• vitamin B-12 deficiency
• radiation therapy involving bone marrow
• phenytoin and sulfa drugs
• chemotherapy medications
• toxins, such as benzenes and insecticides
• aplastic anemia, when the bone marrow stops producing enough blood cells
• severe congenital neutropenia, a group of disorders where neutrophils cannot mature
• cyclic neutropenia, which causes cell levels to rise and fall
• chronic benign neutropenia, which causes low cell levels for no apparent reason

Testing

Doctors can identify changes in neutrophil levels from a blood test called a complete blood count (CBC) with differential, which identifies specific groups of white blood cells.

A doctor may order a CBC test when someone is experiencing a range of symptoms related to infection, chronic illness, and injury, such as fever, pain, and exhaustion. A nurse or technician will draw a small amount of blood from the arm and send it off for evaluation.

If the initial test shows a higher or lower number of white blood cells than normal, the doctor will likely repeat the test to confirm the results. If the initial results are confirmed, a doctor will perform a physical exam, ask questions about the person’s lifestyle, and review their medical history.

If there is no apparent reason for changes in white blood cell levels, the doctor will order a more specific test. Laboratory specialists will look for specific white blood cells, such as immature neutrophils called myeloblasts. During an infection or chronic illness, these cells emerge from the bone marrow and mature in the blood instead of the bone marrow.

If myeloblasts or other white blood cells appear in significant levels in the blood, the doctor will request a bone marrow sample.

Bone marrow collection involves inserting a long needle into part of the pelvis near the back of your hip. The procedure can be very painful, and a doctor will typically take the sample in a hospital setting with at least a local anesthetic.

Experts will examine the bone marrow sample to see if neutrophils and other blood cells are developing correctly and are in regular supply.

If the cause of the high or low neutrophil levels is still uncertain, the doctor will order other tests to try to pinpoint the cause of the changes, such as:

• CT scans
• blood cultures
• urine sample analysis
• a chest X-ray