Your blood counts — the numbers of different types of blood cells in your body — can help you better understand your health. Sometimes, having too many or type few types of blood cells can lead to certain health conditions. For example, leukocytosis is the medical term for high levels of white blood cells (WBCs). Leukocytosis can be a sign of leukemia, though there are many other more common and less serious reasons why a person with may have elevated WBC numbers.

If you’re living with leukemia, your WBC levels can help your doctors better understand your prognosis (outlook) and determine which treatments are most likely to be effective.

Testing White Blood Cell Levels

WBCs are a part of your immune system. They help find and attack germs that cause infection. WBCs are made in the bone marrow (the soft, spongy tissue found inside certain bones).

Levels of WBCs are measured using a test called a complete blood count (CBC). This test also measures levels of other blood cells, such as red blood cells and platelets. CBCs are carried out using a small sample of your blood. You may get undergo a CBC test during an annual physical exam to check for general health problems. Your doctor may also recommend this test if they suspect you have a condition that affects your blood cells.

WBC levels are normally between 4,500 and 11,000 cells per microliter. (What is considered a normal range may vary depending on the lab that conducted your test.) If your WBC counts are higher than 11,000 cells per microliter, you have leukocytosis. Talk to your health care provider about interpreting your laboratory test results.

A CBC also measures the specific types of WBCs — basophils, eosinophils, lymphocytes, monocytes, and neutrophils. If you have high levels of one of these types of WBCs, you may be diagnosed with a certain type of leukocytosis. For example, having high levels of eosinophils is known as eosinophilia, and having too many lymphocytes is called lymphocytosis.

What Do High WBC Counts Mean?

Various conditions can affect WBC levels. You might have a low WBC count due to:

• Liver disease
• Autoimmune disorders — Conditions in which the immune system attacks the healthy tissues
• A genetic trait
• Medications

Most often, infections cause high WBC levels. WBCs are important for fighting off bacteria and viruses, so your bone marrow makes more of them when these germs enter your body. You may be fighting off an infection if you have high WBC counts in addition to other infection symptoms such as fever, coughing, sinus congestion, sore throat, pain, urination changes, or diarrhea.

Other causes of leukocytosis include:

• Allergies
• Immune system disorders that cause inflammation such as rheumatoid arthritis or lupus
• Tissue damage from burns or other injuries
• Thyroid conditions
• Tooth decay or cavities
• Cigarette smoke
• Pregnancy
• High stress levels
• Splenectomy (surgery to remove your spleen)
• Obesity

Too many WBCs can also be a sign of blood cancer such as leukemia or lymphoma. However, this is rare.

High WBC counts may also be a drug side effect. Medications that boost WBC levels include:

• Corticosteroids — Medications that help treat inflammation
• Beta-agonists — Drugs prescribed for lung conditions like asthma or chronic obstructive pulmonary disease
• Epinephrine — A medication used for asthma, severe allergic reactions, heart attacks, and eye surgery
• Heparin — A treatment that helps prevent blood clots
• Lithium — A medication that treats depression and bipolar disorder

If you had abnormally high levels of white blood cells on a CBC, ask your doctor if there is any cause for concern. Leukocytosis is not often a sign of a serious issue.

When Is Leukocytosis a Sign of Leukemia?

In some cases, leukocytosis is a leukemia symptom. You can’t tell from a CBC alone what’s causing your leukocytosis, but there may be other indications that you could have leukemia.

Other symptoms that could signal leukemia include:

• Fever or night sweats
• Tiredness or weakness
• Unexpected weight loss
• Bone pain
• Frequent bruising
• Bleeding problems such as nosebleeds, bleeding gums, or a heavy menstrual period
• Enlarged lymph nodes, which may feel like hard lumps in your neck, armpit, or groin
• An enlarged spleen or liver, which may appear as pain or a feeling of fullness in your abdomen

Tell your doctor if you have any of these symptoms, especially if your WBC counts are high. If your doctor wants to examine your blood cells further to look for problems, they may recommend additional diagnostic tests. These blood tests can help confirm or rule out leukemia.

Your health care team may use blood samples to perform a peripheral blood smear, which entails studying your blood cells closely under a microscope. Your blood samples may also be used for a flow cytometry test, during which your cells are checked for certain proteins that could indicate they are cancerous. Leukemia can also be diagnosed with a bone marrow biopsy, in which a small sample of bone marrow is removed and tested for cancer.

What Does Your WBC Count Tell You About Leukemia?

If you have been diagnosed with leukemia, your doctor will likely have you undergo regular CBC testing. This can provide information about your treatment and outlook.

Having very high numbers of WBCs when you’re first diagnosed may be a sign that you have faster-growing leukemia. This is true for various types of leukemia, including acute myeloid leukemia, acute lymphoblastic leukemia, chronic myeloid leukemia, and chronic lymphocytic leukemia. People with many WBCs may have a worse outlook — they may be less likely to go into remission (have their cancer go away) and more likely to have their leukemia return or progress.

However, doctors take this information into account when recommending treatment plans. Your doctor may recommend more aggressive leukemia treatments, although this could cause additional side effects.

WBC counts also show how well treatment is working. If your treatment plan is successful, your WBC levels should return to normal.

Talk With Others Who Understand

MyLeukemiaTeam is the social network for people with leukemia and their loved ones. On MyLeukemiaTeam, more than 12,000 members come together to ask questions, give advice, and share their stories with others who understand life with leukemia.

Are you living with leukemia? Do you have high WBC levels? Share your experiences in the comments below, or start a conversation by posting on your Activities page.