How Is Chronic Myeloid Leukemia Diagnosed?

Many people with CML do not have symptoms when it is diagnosed. The leukemia is often found when their doctor orders blood tests for an unrelated health problem or during a routine checkup. Even when symptoms are present, they are often vague and non-specific.

If signs and symptoms suggest you may have leukemia, the doctor will need to check samples (specimens) of blood and bone marrow to be certain of this diagnosis. Blood is usually taken from a vein in the arm. Bone marrow is obtained through a procedure called a bone marrow aspiration and biopsy. These samples are sent to a lab, and they are looked at under a microscope for leukemia cells.

Doctors will look at the size and shape of the cells in the samples and whether they contain granules (small spots seen in some types of white blood cells). An important factor is whether the cells look mature (like normal circulating blood cells) or immature (lacking features of normal circulating blood cells). The most immature cells are called myeloblasts (often just called blasts). An important feature of a bone marrow sample is how much of it is blood-forming cells. This is known as cellularity. Normal bone marrow contains both blood-forming cells and fat cells.

When the bone marrow has more blood-forming cells than expected, it is said to be hypercellular. If too few of these cells are found, the marrow is called hypocellular.

In people with CML, the bone marrow is often hypercellular because it is full of leukemia cells. These tests may also be done after treatment to see if the leukemia is responding to treatment.

Lab tests

One or more of the following lab tests may be used to diagnose CML or to help determine how advanced the disease is.

Blood cell counts and blood cell exam

The complete blood count (CBC) is a test that measures the levels of different cells, like red blood cells, white blood cells, and platelets, in the blood. The CBC often includes a differential (diff), which is a count of the different types of white blood cells in the blood sample. In a blood smear, some of the blood is put on a slide to see how the cells look under the microscope.

Most patients with CML have too many white blood cells with many early (immature) cells. Sometimes CML patients have low numbers of red blood cells or blood platelets. Even though these findings may suggest leukemia, this diagnosis usually needs to be confirmed by another blood test or a test of the bone marrow.

Blood chemistry tests

These tests measure the amount of certain chemicals in the blood, but they are not used to diagnose leukemia. They can help find liver or kidney problems caused by the spread of leukemia cells or by the side effects of certain chemotherapy drugs. These tests also help determine if treatment is needed to correct low or high blood levels of certain minerals.

Genetic tests

Some sort of gene testing will be done to look for the Philadelphia chromosome and/or the BCR-ABL gene. This type of test is used to confirm the diagnosis of CML.

Conventional cytogenetics

This test looks at chromosomes (pieces of DNA) under a microscope to find any changes. It is also called a karyotype. Because chromosomes can best be seen when the cell is dividing, a sample of blood or bone marrow has to be grown (in the lab) so that the cells start to divide. This takes time, and is not always successful.

Normal human cells have 23 pairs of chromosomes, each of which is a certain size. The leukemia cells in many CML patients contain an abnormal chromosome known as the Philadelphia chromosome, which looks like a shortened version of chromosome 22. It is caused by swapping pieces (translocation) between chromosomes 9 and 22 (see Do We Know What Causes Chronic Myeloid Leukemia?). Finding a Philadelphia chromosome is helpful in diagnosing CML. Even when the Philadelphia chromosome can't be seen, other tests can often find the BCR-ABL gene.

Fluorescent in situ hybridization

Fluorescent in situ hybridization (FISH) is another way to look at chromosomes. This test uses special fluorescent dyes that only attach to specific genes or parts of chromosomes. In CML, FISH can be used to look for specific pieces of the BCR-ABL gene on chromosomes. It can be used on regular blood or bone marrow samples without culturing the cells first, so the results can come back more quickly than with conventional cytogenetics.

Polymerase chain reaction (PCR)

This is a super-sensitive test that can be used to look for the BCR-ABL oncogene in leukemia cells. It can be done on blood or bone marrow samples and can detect very small amounts of BCR-ABL, even when doctors can't find the Philadelphia chromosome in bone marrow cells with cytogenetic testing.

PCR can be used to help diagnose CML and is also useful after treatment to see if copies of the BCR-ABL gene are still there. If copies of this gene are still present it means that the leukemia is still present, even when the cells aren't detectable with a microscope.

Imaging tests

Imaging tests produce pictures of the inside of the body. They are not needed to diagnose CML, but sometimes may be done to look for the cause of symptoms or to see if the spleen or liver are enlarged.

Computed tomography scan

A CT scan can help tell if any lymph nodes or organs in your body are enlarged. It isn’t usually needed to diagnose CML, but it may be done if your doctor suspects the leukemia is growing in an organ, like your spleen.

In some cases, a CT can be used to guide a biopsy needle precisely into a suspected abnormality, such as an abscess. For this procedure, called a CT-guided needle biopsy, you remain on the CT scanning table while a radiologist moves a biopsy needle through the skin and toward the location of the mass. CT scans are repeated until the needle is within the mass. A sample is then removed to be looked at under a microscope. This is rarely needed in CML.

Magnetic resonance imaging scan

Magnetic resonance imaging (MRI) scans are very helpful in looking at the brain and spinal cord. 


Ultrasound can be used to look at lymph nodes near the surface of the body or to look for enlarged organs inside your abdomen such as the kidneys, liver, and spleen. This is an easy test to have, and it doesn't use radiation. For most scans you simply lie on a table, and a technician moves the transducer over the part of your body being looked at.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master's-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: February 24, 2015 Last Revised: February 22, 2016

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