Tests for Chronic Myelomonocytic Leukemia (CMML)

If your doctor suspects you might have chronic myelomonocytic leukemia (CMML), they will do tests to learn more.

Some people have symptoms that suggest they might have CMML. In other people with CMML, the first sign is an abnormal blood test result.

In either case, your doctor will test cells from your blood to see if you have CMML (or some other type of blood cancer). The doctor will most likely test cells from your bone marrow as well. If you do have CMML, these tests can also help the doctor learn more about it.

Blood tests for CMML

The doctor will most likely order a test called a complete blood count. Other blood tests might also be done.

Complete blood count

A complete blood count (CBC) measures the levels of red blood cells, white blood cells, and platelets in your blood. The CBC is often done with a differential count (or “diff”). This is a count of the different types of white blood cells in the blood sample.

A complete blood count can tell the doctor if you have:

• High numbers of monocytes: People with CMML typically have high numbers of monocytes, (at least 500 per mm³ of blood). Monocytes are a type of white blood cell.
• Low numbers of other cells: People with CMML also often have low numbers of other white blood cells, red blood cells, and/or blood platelets.
• Monoblasts: Some people with CMML have monoblasts (sometimes just called 'blasts') in their blood. Monoblasts are very early forms of monocytes. Normally, these cells are only found in the bone marrow. It's never normal to see blasts in the blood, and it's often a sign of a bone marrow problem.
• Changes in your blood cells: Blood cells in people with CMML may also have certain changes in size, shape, or other features that can be seen with a microscope.

Other blood tests

There are other possible causes of low blood counts, such as low levels of vitamin B12 and folate. Your doctor might do other blood tests to check for these causes.

Blood tests may also be done to look for other causes of a high white blood cell count, such as an infection.

Bone marrow tests for CMML

If your doctor suspects you might have some type of blood cancer (such as a leukemia), they might also test your bone marrow.

For this testing, samples of your bone marrow will be taken during a bone marrow aspiration and biopsy. The samples are usually taken from the back of your pelvic (hip) bone.

These tests can be used to help diagnose and classify the type of blood cancer you have. They may also be repeated later to see if treatment is working or if the CMML is transforming into an acute (fast-growing) leukemia.

Bone marrow aspiration and biopsy

For a bone marrow aspiration, you lie on a table (either on your side or on your belly). After cleaning the skin over your hip, the surface of the bone is numbed with local anesthetic using a very thin needle. This may cause a brief stinging or burning sensation.

A long, hollow needle is then put into the bone, and a syringe is used to suck out a small amount of liquid bone marrow. Even with the anesthetic, most people still feel some brief pain when the marrow is removed.

A bone marrow biopsy is usually done right after the aspiration. A small core of bone and marrow is removed with a wider needle that's pushed into your hip bone. The biopsy also causes some brief pain. Once the biopsy is done, pressure on the area will help prevent bleeding and bruising.  

Looking at the cells in the bone marrow

A pathologist will examine your bone marrow samples with a microscope. A pathologist is a doctor trained in diagnosing diseases using lab tests. Other doctors may look at the samples, too.

The doctors will look at the types and number of blood-forming cells in your bone marrow. They will also check to see if the bone marrow shows signs of infections, cancer cells, or other disorders.

They will look at the size and shape of the cells to figure out if the red cells contain iron particles or if the white blood cells contain granules (microscopic collections of enzymes and other chemicals that help them fight infections).

Measuring blasts

Tests will be done to measure the percentage of marrow cells that are blasts.

Blasts are very early forms of blood cells that are made by bone marrow stem cells. Over time, blasts mature into normal blood cells. But in CMML, some of the blasts don't mature properly, so there may be too many blasts and not enough mature cells.

For a diagnosis of CMML, there must be less than 20% blasts in the bone marrow. If there are more than 20% blasts in the bone marrow, a person has an acute leukemia instead.

Cytogenetic testing

This test (sometimes called karyotyping) looks at the chromosomes inside your bone marrow cells. Each cell should have 46 chromosomes (23 pairs). DNA, which makes up our genes, is packed into chromosomes.

Chromosome changes are fairly common in CMML cells, although there's no single chromosome change that everyone with CMML has.

• Sometimes pieces of chromosomes or even whole chromosomes are missing (known as a deletion).
• CMML cells may also have extra copies of all or part of some chromosomes (known as an addition or duplication).
• Chromosome translocations (where parts of chromosomes trade places with each other) may also be seen in CMML cells.

Chromosome testing can also help the doctors confirm that you have CMML and not a different type of leukemia.

For example, in chronic myeloid leukemia (CML), the leukemia cells often have an abnormal chromosome caused by a certain translocation. This is called the Philadelphia chromosome or BCR/ABL1 fusion. If the Philadelphia chromosome is present, the diagnosis is CML, not CMML.

Finding changes in certain other genes also makes it very unlikely that a person has CMML.

Cytogenetic testing can take a week or longer because the bone marrow cells need time to grow in lab dishes before the chromosomes can be seen with a microscope.

Fluorescence in situ hybridization (FISH)

Another test option for looking at chromosomes is fluorescence in situ hybridization (FISH). This test uses special fluorescent dyes that only attach to specific parts of chromosomes.

FISH can find most chromosome changes (such as translocations and deletions) that can be seen with standard cytogenetic tests. It can also find some changes that are too small to be seen with usual cytogenetic testing. FISH is very accurate, and results are often available within a couple of days.

Other bone marrow tests

Other bone marrow tests can help your doctor diagnose CMML and rule out other blood diseases. For example:

• Immunocytochemistry can be helpful in distinguishing CMML from other types of leukemia and from other diseases.
• Flow cytometry can be very helpful in diagnosing leukemias and lymphomas.
• Molecular genetic tests aren't usually needed to diagnose CMML, but they can still be helpful in some cases.

These tests can also be done on cells from your blood. For more on these lab tests, see Tests Used on Biopsy and Cytology Samples to Diagnose and Classify Cancer.