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.
There are many different reasons why a person may have higher or lower than normal levels of neutrophils in their blood.
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
- genetic conditions, such as Down syndrome
- surgical removal of the spleen
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:
- 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
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
Changes in neutrophil levels are often a sign of more significant changes in white blood cell levels.
The amount and proportion of white blood cells in the bloodstream change over time with age and other events, such as pregnancy. While everyone's normal range is slightly different, some commonly used ranges include:
- Newborn: 13,000 to 38,000 per mm3
- Infant 2 weeks of age: 5,000 to 20,000 per mm3
- Adult: 4,500 to 11,000 per mm3
- Pregnant female (third trimester): 5,800 to 13,200 per mm3
In non-pregnant adults, a white blood cell blood count over 11,000 per mm3 is known as leukocytosis, which is an elevated white blood cell count. Neutrophilic leukocytosis occurs when a person has over 7,000 per mm3 mature neutrophils in their bloodstream.
The lower blood level limit for neutrophils in human blood is 1,500 per mm3. When a person's levels of neutrophils are low, it is known as neutropenia. The lower the level of neutrophils circulating in the blood, the more severe neutropenia. Neutropenia levels are:
- Mild neutropenia: 1,000 to 1,500 per mm3
- Moderate neutropenia: 500 to 999 per mm3
- Severe neutropenia: 200-499 per mm3
- Very severe neutropenia: below 200 per mm3
Minor changes in neutrophil or white blood cell levels are typically nothing to worry about as long as they are temporary. A raised white blood cell count often means the body is responding to infection, injury, or stress.
Some people have naturally lower levels of white blood cells and neutrophils than other people due to a range of factors, including congenital conditions.
If neutrophil or white blood cell levels are significantly altered for no apparent reason or remain raised or lowered, a doctor will order more tests to determine the cause.
Severely high or low levels of white blood cells often require emergency care and monitoring. People with severe neutropenia will have an inadequate defense against infection.
People with severe neutrophilia typically have a life-threatening type of infection or other inflammatory illness that requires treatment, such as cancer.
The best way to correct abnormal neutrophil levels is to address and treat the underlying cause.
Antibiotics can treat bacterial infections, while antifungal medicine treats fungal infections. People can treat certain viral infections with medications that slow viral activity. Otherwise, supportive therapies, such as fluids and rest, may be part of the treatment plan.
People with altered neutrophil levels caused by medications or procedures may need to stop or adjust treatments.
People with chronic conditions that disrupt adequate neutrophil production or maturation may need to take drugs that allow the body to raise neutrophil production, such as:
- colony-stimulating factors
- anti-thymocyte globulin
- bone marrow or stem cell transplantation
People with severely low levels of neutrophils often require monitoring, antibiotic therapy, and hospitalization to reduce the risk of severe infection.
This period of intensive care helps keep people with weakened immune systems away from potentially harmful microorganisms. It also supports the body, giving it time to produce more white blood cells.
One of the causes of low neutrophil blood levels is a vitamin B-12 deficiency. Eating foods rich in B-12 may help improve low neutrophil blood levels. Examples of foods rich in vitamin B-12 include:
- milk and other dairy products
- many fortified breakfast cereals and bread products
- fortified nutritional yeast products
To help reduce the risk of high or low neutrophil levels, people may want to try the following tips:
- Try not to over-exercise or exercise beyond comfort levels.
- Reduce stress levels and treat chronic or severe stress.
- Seek medical attention for signs of infection, such as fever, weakness, fatigue, or pain, and treat infections exactly as prescribed.
- Follow a healthful, balanced diet.
- Eat enough protein.
- Treat chronic conditions, such as genetic or inflammatory conditions, exactly as prescribed.
However, people with only minor or mild changes in their neutrophil blood levels often show no symptoms and do not require any treatment.
Having a healthy number of neutrophils in the blood and bone marrow is crucial to the correct working of the immune system.
When neutrophil levels are higher or lower than usual for more than a short period, a doctor will order several tests to work out the underlying cause. People with significantly altered neutrophil levels may also require hospitalization to prevent infection and treat life-threatening conditions.
Neutrophilia, when neutrophil levels that are higher than usual are often related to:
- physical or emotional stress
- medication use
- inflammatory conditions
Neutropenia, where neutrophil levels are lower than usual are often related to:
- severe or chronic infections
- drug therapy
- vitamin deficiencies
- genetic conditions
It is a good idea to have regular wellness checks at a doctor's office to stay on top of health. Anyone with concerns about their neutrophil count or any medical condition should talk to their doctor who will be able to answer questions they may have.