What Are Neutrophils?

Medically Reviewed by Zilpah Sheikh, MD on May 13, 2024
Written by Angela McPhillips
7 min read

Neutrophils are an important part of your immune system. They’re a type of white blood cell that kills and eats bacteria and fungi to help your body fight infections and heal wounds. There are many types of cells in your blood, but neutrophils make up the biggest number of all kinds of white blood cells. 

Neutrophils function

The main job of neutrophils is to help your body fight infections and heal wounds. Bacteria, viruses, and fungi are germs that can cause infections in your body. Neutrophils travel to the source of an infection and ingest or break down these germs. They work with other immune cells in your body to fight infections and heal injuries. 

White blood cells make up about 1% of your body's total blood cells and are an important part of your immune system. Neutrophils are the cells that respond first to any type of infection or wound. These make up 50% to 75% of your white blood cells. Neutrophils are made in your bone marrow. They live less than a day, so your bone marrow constantly makes new ones.

If your doctor thinks your neutrophil count may be low or high, they may order a blood test.

Complete blood count test

Your doctor will likely start with a test called a complete blood count (CBC) with differential. The CBC with differential tells how many of each type of blood cell is in your blood.

Absolute neutrophil count test

The differential part of the CBC test tells how many of each type of white blood cell is in your blood. This includes an absolute neutrophil count (ANC). The ANC tells how many neutrophils are in your blood.  

Neutrophils normal range

Normal neutrophil counts depend on different factors such as age — but generally, a normal neutrophil level is between 2,500 and 7,000 neutrophils per microliter. A low neutrophil level is less than 45% of your total white blood cells or 1,500 neutrophils per microliter. A high neutrophil level is over 7,700 neutrophils per microliter. 

What is neutrophilic leukocytosis?

A high neutrophil count is called neutrophilia or neutrophilic leukocytosis. Neutrophilic leukocytosis is when your neutrophil count is above 11,000 cells per microliter. It can be caused by a lot of different conditions, including: 

Infection. This is the most common cause of a high neutrophil count. Most bacterial infections cause a high neutrophil count, but not all of them do. Viral infections don't generally cause neutrophilia, but they may in the early stage of infection. Some fungal and parasitic infections can cause neutrophilia as well.

Inflammation. Any condition that causes inflammation in your body can increase your neutrophil count. Examples of this include:

  • Rheumatoid arthritis and gout, which are types of arthritis
  • Ulcerative colitis, which is irritation and ulcers in your large intestine
  • Tissue damage from burns, surgery, or trauma
  • Loss of blood
  • Sickle cell crisis, which is a type of red blood cell disorder
  • Acute kidney failure
  • Diabetic ketoacidosis, a serious complication of diabetes when acids build up in your blood
  • Cushing syndrome, which is when your body has too much cortisol
  • Preeclampsia and eclampsia, which are complications of pregnancy that can cause organ damage
  • Heart attack
  • Acute hypoxia, which is a lack of oxygen

Medicines. Some medicines can cause neutrophilia, such as:

  • Lithium, a mood stabilizer
  • Heparin, a blood thinner
  • Antiseizure drugs to treat seizures or epilepsy
  • Minocycline, an antibiotic 
  • Clozapine to treat schizophrenia
  • Corticosteroids to treat inflammation

Some types of cancer. Cancers that can cause neutrophilia include:

The treatment for neutrophilia involves treating the underlying cause. A high neutrophil count isn't a problem on its own. Your doctor will do tests to find out what is causing you to have neutrophilia and treat that. 

Symptoms of neutrophilia depend on the underlying cause. If you have a high neutrophil count because of inflammation, infection, medication side effects, or cancer, you may have the following symptoms:

  • Fever of 100.4 degrees F or higher
  • Infections that keep coming back
  • Wounds that don’t heal
  • Swollen or aching joints
  • Feeling tired or weak
  • Dizziness or fainting

What is neutropenia?

A low neutrophil count is called neutropenia. Neutropenia may be mild, moderate, or severe depending on the number of neutrophils in your blood.

You can be born with neutropenia (called congenital) or develop the condition over time (called acquired). Neutropenia may also be temporary or long-lasting, depending on the cause. 

Since neutrophils are cells that are part of your immune response to fight infections, neutropenia can make you more likely to get an infection. If you have severe neutropenia, even normal bacteria on your body can cause serious infections. 

There are many different conditions and some medications that can cause neutropenia. 

Cancers and cancer treatment. Blood cells, including neutrophils, are made in your bone marrow. Cancers that affect your bone marrow, such as lymphoma, leukemia, and myeloma, can cause neutropenia. Chemotherapy and radiation prevent your body from producing neutrophils, so neutropenia is an expected side effect of this cancer treatment. 

Infections. Some types of infections can cause neutropenia, such as:

Sepsis, which is an extreme response your body can have to an infection, can also lead to neutropenia.‌

Medicines. Many medicines have been linked with neutropenia. This is called drug-induced neutropenia and usually happens within 6 months of starting the medicine. Once you quit taking the medicine, the neutropenia usually clears up within 1 week.

Some of these medicines include:

  • Antibiotics such as cephalosporins, penicillin, and vancomycin
  • Antiviral medicines such as ganciclovir and valganciclovir
  • Medicines to treat overactive thyroid such as methimazole 
  • Antiseizure medicines such as mephenytoin phenytoin, trimethadione, and valproic acid 
  • Antidepressants and antipsychotic medicines 
  • Anti-inflammatory medicines such as ibuprofen
  • Antimalarial medicines such as hydroxychloroquine 
  • Medicines to treat irregular heart rhythms 

Bone marrow disorders. Conditions that affect your bone marrow such as aplastic anemia, myelodysplastic syndrome, and myelofibrosis can cause neutropenia. 

Nutritional deficiencies. Not getting enough copper, folate, or vitamin B12 in your diet can cause neutropenia. 

Autoimmune disorders. Conditions like Crohn’s disease, lupus, and rheumatoid arthritis make antibodies that destroy healthy neutrophils, which can lead to neutropenia.

The treatment of neutropenia will depend on its cause and severity. It's important to treat any source of infection in people with neutropenia. If you have neutropenia and fever, your doctor may treat you with antibiotics even if no source of infection can be found. If your doctor thinks your medicine may be causing neutropenia, they may switch your prescription to a different medicine.

You may be given medicine that will stimulate your body to make more white blood cells. If you have an autoimmune disorder that is causing your neutropenia, your doctor may prescribe corticosteroids. If your neutropenia is caused by an underlying condition, treatment of it may clear up the neutropenia. 

Neutropenia does not cause any symptoms. But the chances of getting an infection if you have neutropenia are very high. If you get an infection because of your low neutrophil count, you may have the following symptoms:

  • Fever
  • Feeling tired or weak
  • Sore throat
  • Swollen lymph nodes, which may feel like small, tender lumps along your neck
  • Sores in your mouth or around your anus
  • Diarrhea
  • Burning when you pee
  • Pain, swelling, or red bumps at the site of a sore or wound

Neutrophils are white blood cells that protect your body from infections and help your body heal from injuries. Many different conditions can cause high or low neutrophil counts in your blood. If you have neutropenia or neutrophilia, your doctor will treat your symptoms and help you manage your condition.

What does it mean when your neutrophils are high?

A high neutrophil count means that you have more than 7,700 neutrophils per microliter in your blood. The normal range is 2,500-7,000.  A high neutrophil count may be caused by infection, inflammation, some types of cancer, or certain medications. 

What is an alarming neutrophil count?

A low neutrophil count, or neutropenia, is less than 1,500 neutrophils per microliter. Neutropenia can be mild, moderate, or severe. A high neutrophil count, or neutrophilia, is more than 7,700 neutrophils per microliter. Both neutropenia and neutrophilia should be monitored by your doctor to figure out and treat the cause. 

What does it mean if your neutrophil count low?

Low neutrophils can be caused by many conditions. If you have a low neutrophil count, you’re at risk of getting an infection. In this case, it’s important to take steps to protect yourself. This includes: 

  • Wash your hands frequently.
  • Avoid large crowds or contact with sick people.
  • Stay up-to-date on vaccines, including flu and COVID-19 if recommended by your doctor.
  • Take medications to prevent infections as prescribed by your doctor.