An unusual white blood cell count can be a sign of chronic myeloid leukemia (CML), a type of blood cancer. CML can affect the balance of white blood cells in the blood and cause them to function incorrectly.

A white blood cell (WBC) count outside the normal range of 4,500–11,000 cells per microliter (μl) of blood can indicate different conditions, including CML. Most people with CML will have too many WBCs, with most of them being immature WBCs known as myeloblasts.

Although a high WBC count, also called leukocytosis, may indicate CML, a doctor will need to perform other blood tests or test the bone marrow to confirm the diagnosis.

In this article, we discuss what WBC count range may indicate CML. We also explain how CLM affects other blood cells and look at the other diagnostic tests a doctor may perform.

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The normal WBC count range is 4,500–11,000/μl. Anything outside those levels may indicate a medical problem. The WBC count range for people with CML is much higher than normal levels.

The median WBC count among people with CML is 100,000/μl, but it can climb higher. Some sources note that people with acute or chronic leukemia may have a WBC count in the 100,000–400,000 range. As high WBC counts may indicate other conditions, doctors will conduct additional tests to help rule out or confirm CML.

WBCs, also known as leukocytes, are an important component of blood. Although they only account for about 1% of a person’s blood, they play an essential role in protecting the body from infections. Bone marrow is the spongy tissue inside some bones that produces WBCs.

CML typically results from changes within the DNA of cells. In most cases, a translocation occurs between chromosomes 9 and 22. This means that the chromosomes swap part of their code.

In this case, the ABL1 gene from chromosome 9 joins to the BCR gene on chromosome 22, forming the BCR-ABL1 fusion gene, which some people also refer to as the Philadelphia chromosome. This gene change is responsible for the growing and rapid dividing of CML cells. It results in the bone marrow producing excess myeloblasts that do not function correctly.

This increase in immature cells raises the WBC count. As these cells do not function normally, the raised count can lead to the development of certain CML symptoms, such as:

  • fatigue
  • night sweats
  • unintentional weight loss
  • bone pain
  • an enlarged spleen

The Leukemia & Lymphoma Society notes that the increase in the number of immature WBCs prevents the bone marrow from making healthy red blood cells (RBCs) and platelets.

Therefore, in addition to increasing the WBC count, CML may cause a decrease in the RBC count. Depending on the phase of CML, the number of platelets may be higher or lower than normal.

The changes to other types of cells in the body may lead to additional symptoms in people with CML. For instance, if the RBC count becomes too low, a person may experience symptoms such as:

  • tiredness
  • shortness of breath
  • weakness

When platelets are low, additional symptoms may develop, including:

  • frequent nosebleeds
  • bleeding gums
  • easy bruising

In addition to checking the WBC count, doctors will likely order additional tests to confirm a suspected diagnosis. A high WBC count is not usually enough to confirm a diagnosis. Other possible diagnostic tests for CML include:

  • Complete blood count: This test measures the number of WBCs, platelets, and RBCs in the blood, as well as the hemoglobin level.
  • Peripheral blood smear: Doctors can use a blood smear to check the size and shape of blood cells, the specific patterns of WBCs, and the percentage of immature WBCs.
  • Bone marrow biopsy: This test involves removing bone marrow, most often from a person’s hip bone. The doctor inserts a needle into the hip bone to remove a marrow sample. The next step involves examining the marrow under a microscope to check for abnormalities and cellular changes.
  • Cytogenetic analysis: This involves a study of chromosomal abnormalities. Doctors examine samples of bone marrow under the microscope to detect chromosome abnormalities, such as the Philadelphia chromosome that is associated with CML.
  • FISH (fluorescence in situ hybridization): This lab test allows medical professionals to examine chromosomes and genes in cells. The FISH test has increased sensitivity in detecting CML and can identify the presence of the BCR-ABL1 gene. It helps confirm a diagnosis of CML.
  • qPCR (quantitative polymerase chain reaction): This test is more sensitive than all the other tests above. It can detect very small quantities of the BCR-ABL1 gene in the bone marrow or blood samples. For instance, it can detect one CML cell out of 100,000 or more normal cells.

Imaging tests, such as a CT scan or ultrasound, do not diagnose CML. However, these types of tests are helpful in identifying enlarged lymph nodes or an enlarged spleen, which may occur with CML.

After diagnosing CML, doctors may recommend that the person periodically undergo tests, such as a bone marrow exam, qPCR, and FISH. The reason for this is that these tests may help monitor how well someone responds to treatment.

Many other conditions can cause a high WBC count. Typically, WBC counts that are very high indicate a more serious condition or cause than levels that are just outside the normal range.

Possible causes of a high WBC count include:

  • infection
  • vaccine administration
  • acute or chronic allergies
  • a heart attack
  • certain medications, such as corticosteroids, epinephrine, and antibiotics
  • acute leukemia
  • connective tissue diseases

As many conditions can cause high WBC counts, doctors will likely use additional tests, a physical exam, and a review of symptoms to confirm a diagnosis.

Learn about the other causes of a high white blood cell count.

White blood cells are an important component of blood, as they help fight infection. The normal WBC count for an adult is within the range of 4,500–11,000/μl. However, when a person has CML, their WBC count is significantly higher and often 100,000/μl or more.

This is because CML affects the bone marrow and causes it to produce an excessive number of immature WBCs. This increase in nonfunctioning WBCs contributes to some of the symptoms of CML.

CML is not the only possible cause of a high WBC count. Due to this, a doctor will perform other tests to help them confirm a diagnosis.