Leukocytosis is condition characterized by increased levels of leukocytes in the blood. Leukocytes are a type of white blood cell that help protect your body against illness and infection.

Although leukocytosis typically occurs when you’re sick, it can also be caused by several other factors, such as stress.

This article will take an in-depth look at some of the types, symptoms, and causes of leukocytosis, along with how to treat and prevent it.

There are five different types of leukocytosis:

  • Neutrophilia. This common type of leukocytosis is caused by an increase in neutrophils, which account for 40–60 percent of the white blood cells (WBC) in your body.
  • Lymphocytosis. This occurs when you have high levels of lymphocytes, which make up 20–40 percent of your white blood cells.
  • Monocytosis. This form of leukocytosis is characterized by high levels of monocytes, which comprise about 2–8 percent of your white blood cells.
  • Eosinophilia. Like monocytosis, this type of leukocytosis is uncommon and is caused when you have a high number of eosinophils, which make up about 1–4 percent of the white blood cells in your body.
  • Basophilia. As the rarest form of leukocytosis, basophilia occurs when you have increased levels of basophils, which only account for 0.1–1 percent of your body’s white blood cells.

Each form of leukocytosis is linked with several health conditions:

  • neutrophilia: inflammation and infections
  • lymphocytosis: leukemia and viral infections
  • monocytosis: cancer and other types of infections
  • eosinophilia: parasites and allergies
  • basophilia: leukemia

When you have very high levels of white blood cells in your body, they can cause your blood to become very thick, which can impair blood flow.

This can lead to a condition called hyperviscosity syndrome. Although it can occur with leukemia, it’s very rare.

This condition can cause several serious issues, including:

  • stroke
  • vision problems
  • difficulty breathing
  • bleeding from the intestines, mouth, or stomach

Leukocytosis can also cause other symptoms. This may be related to the effects of the specific type of white blood cell that’s elevated or any underlying health conditions that cause leukocytosis.

Some common symptoms include:

  • fever
  • pain
  • easy bruising
  • difficulty breathing
  • wheezing
  • hives and itching
  • weight loss
  • night sweats

Keep in mind that you may not experience any symptoms if your leukocytosis is caused by stress or a reaction to a medication.

The causes of leukocytosis can be categorized by the specific type of white blood cell that’s elevated.

Some of the common causes of neutrophilia include:

  • infections
  • smoking
  • certain types of leukemia
  • emotional or physical stress
  • having your spleen removed
  • a reaction to medications, including steroids, lithium, or certain types of inhalers
  • chronic inflammation caused by injuries, arthritis, or other inflammatory conditions

A few potential causes of lymphocytosis include:

  • allergic reactions
  • pertussis, or whooping cough
  • certain types of leukemia
  • viral infections

Some of the main causes of eosinophilia include:

  • allergies and allergic reactions, such as hay fever and asthma
  • parasitic infections
  • certain types of skin diseases
  • lymphoma, or cancer of the lymphatic system

Possible causes of monocytosis include:

Causes of basophilia include:

  • leukemia
  • bone marrow cancer
  • allergic reactions (rarely)

It’s normal for pregnant people to have high levels of white blood cells.

These levels typically increase slowly throughout pregnancy. During the last trimester of pregnancy, the WBC count is usually between 5,800 and 13,200 per microliter of blood.

Not only that, but the stress caused by labor and delivery can also increase levels of white blood cells.

The WBC count also remains slightly above normal for a while after the baby is born and is usually around 12,700 per microliter of blood.

Normal white blood cell levels typically range from 4,500 and 11,000 per microliter of blood for most healthy adults who aren’t pregnant.

Having white blood cell levels above this range can be a sign of leukocytosis.

If you have WBC counts between 50,000 and 100,000 per microliter of blood, it may mean that you have a severe infection, organ rejection, or a solid tumor.

Very high WBC counts over 100,000 generally only occur with conditions like leukemia or other types of blood and bone marrow cancer.

Three different types of tests are commonly used to help determine why you may have increased levels of white blood cells:

  • Complete blood count (CBC) with differential. This is the most common test that’s conducted when your WBC count is higher than normal. This test uses a machine to determine the percentage of each specific type of WBC from a blood sample.
  • Peripheral blood smear. When you have neutrophilia or lymphocytosis, your doctor may perform this test, which can look at the form and maturity of all blood cells. This test may or may not confirm the type of leukocytosis. If there are immature WBCs, it may lead to bone marrow biopsy. This test involves smearing a thin layer of blood onto a glass slide and using a microscope to view the cells.
  • Bone marrow biopsy. This test is used to differentiate leukemia from benign causes. It involves taking a sample of your bone marrow — the tissue that produces WBCs — from the middle of a bone using a needle and looking at it under a microscope. This helps determine if there are any abnormal cells or an issue with the production of WBCs in the bone marrow.

The treatment for leukocytosis can vary depending on its specific cause. Some of the most common treatment options include:

  • antihistamines for allergic reactions
  • inhalers for asthma
  • antibiotics for bacterial infections
  • cancer treatments like chemotherapy, radiation, or stem cell transplants for leukemia
  • medications to treat stress or anxiety
  • treatment for inflammatory conditions
  • changing medications to prevent adverse reactions to certain drugs

If you have hyperviscosity syndrome, treatment may involve the use of intravenous fluids and medications to help quickly decrease your WBC levels and improve blood flow.

There are several ways that you can prevent leukocytosis, including:

  • maintaining a healthy, active lifestyle
  • practicing proper hygiene and handwashing to prevent infection
  • avoiding potential allergens
  • not smoking
  • taking medications for any health conditions as directed by your doctor
  • reducing stress levels
  • seeking treatment for anxiety or mental health issues as needed

Keep in mind that leukocytosis is a normal immune response designed to protect against infection and illness, which means that it’s not always a cause for alarm.

Furthermore, it can also be caused by many other factors, including pregnancy, stress, or intense exercise.

Still, it could be a sign of a more serious issue like leukemia or cancer, so it’s important to work with your doctor to determine the cause and evaluate whether treatment is necessary.