Tests for Chronic Myeloid Leukemia

Many people with chronic myeloid leukemia (CML) don't have symptoms when it's diagnosed. The leukemia is often found when their doctor orders blood tests for an unrelated health problem or during a routine check-up. Even when symptoms are present, they're often vague and non-specific.

Lab tests

If signs and symptoms suggest you may have leukemia, the doctor will need to check your blood and bone marrow to be certain of this diagnosis. Blood is usually taken from a vein in your arm. A small amount of bone marrow is removed with a bone marrow aspiration and biopsy. These samples are sent to a lab, where they're checked under a microscope for leukemia cells.

Blood cell counts

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 your blood. The CBC often includes a differential (diff), which is a count of the different types of white blood cells in your blood sample. In a blood smear, some of your blood is put on a slide to see how the cells look under the microscope.

Most people with CML have too many white blood cells with a lot of early (immature) cells called myeloblasts or blasts. Doctors will look at the size and shape of the cells 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). 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.

Bone marrow samples

Leukemia starts in the bone marrow, so checking the bone marrow for leukemia cells is a key part of testing for it. Bone marrow samples are obtained from 2 tests that are usually done at the same time:

• Bone marrow aspiration
• Bone marrow biopsy

The samples are usually taken from the back of the pelvic (hip) bone, but sometimes other bones are used instead. If only an aspiration is to be done, it may be taken from the sternum (breast bone).

For a bone marrow aspiration, you lie on a table (either on your side or on your belly). The doctor will clean the skin over the hip and then numb the area and the surface of the bone by injecting a local anesthetic. This may cause a brief stinging or burning sensation. A thin, hollow needle is then inserted into the bone, and a syringe is used to suck out a small amount of liquid bone marrow. Even with the anesthetic, most patients still have some brief pain when the marrow is removed.

A bone marrow biopsy is usually done just after the aspiration. A small piece of bone and marrow is removed with a slightly larger needle that is pushed down into the bone. This may also cause some brief pain. Once the biopsy is done, pressure will be applied to the site to help prevent bleeding.

These bone marrow tests are used to help diagnose leukemia, but they might also be repeated later to tell if the leukemia is responding to treatment.

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.

If your bone marrow has more blood-forming cells than expected, it's 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's full of leukemia cells. These tests may also be done after treatment to see if the leukemia is responding to treatment.

Blood chemistry tests

These tests measure the amount of certain chemicals in your blood, but they're 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 drugs. These tests also help determine if you need to be treated 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 a CML diagnosis and learn more about your CML cells.

Conventional cytogenetics

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

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 called the Philadelphia (Ph) chromosome, which looks like a shortened version of chromosome 22. It's caused by swapping pieces (translocation) between chromosomes 9 and 22. (See What Causes Chronic Myeloid Leukemia? for more on this.) Finding a Ph chromosome is helpful in diagnosing CML. But even when the Ph chromosome can't be seen, other tests can often find the BCR-ABL gene. Other chromosome changes can be found with cytogenetic testing, too.

Fluorescent in situ hybridization (FISH)

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 growing the cells first, so you get the results 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 gene in leukemia cells and measure how much is there. 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. It's also useful after treatment to see if copies of the BCR-ABL gene are still there. If copies of this gene are found it means that the leukemia is still present, even when the cells can't be seen with a microscope.

Imaging tests

Imaging tests are used to get pictures of the inside of your body. They aren't needed to diagnose CML, but are sometimes used to look for the cause of symptoms or to see if the spleen or liver are enlarged.

Computed tomography (CT) scan

A CT scan can show if any lymph nodes or organs in your body are enlarged. It isn’t 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 your skin and toward the mass. CT scans are repeated until the needle is in the mass. A sample is then removed and looked at with a microscope. This is rarely needed in CML.

Magnetic resonance imaging (MRI)

MRIs are very helpful in looking at the brain and spinal cord. 

Ultrasound

Ultrasound can be used to look at lymph nodes near the surface of your body or to look for enlarged organs inside your abdomen (belly) such as the kidneys, liver, and spleen.