Diagnosing chronic myeloid leukemia (CML) and its phase usually involves performing a series of tests. Blood tests and bone marrow tests are the most common tests doctors use.
Your doctor needs to test your blood to make a diagnosis. Your blood is sent to a lab for:
- a complete blood count (CBC), which shows the number of red cells, white cells and platelets in your blood. If you have CML, you'll have a lower-than-normal red cell count and an abnormal number of platelets (either too high or too low). Your white cell count will be higher than normal, often reaching very high levels.
- a blood cell examination, which shows whether you have leukemic blast cells and marrow cells called promyelocytes in your blood. If you have CML, you'll also have a high proportion of white cells called myelocytes and neutrophils. (Healthy people don't have these blast cells, promyelocytes and myelocytes in their blood.)
Bone Marrow Tests
Your doctor or oncologist (cancer specialist) will test your bone marrow. Bone marrow testing involves two steps usually done at the same time in a doctor's office or a hospital:
- a bone marrow aspiration to remove a liquid marrow sample
- a bone marrow biopsy to remove a small amount of bone filled with marrow
- measure the number and structure of the chromosomes
- confirm blood test findings
- determine if there is a chromosome abnormality, such as the Ph chromosome
Lab Tests to Confirm a Diagnosis
After your doctor takes samples of your blood and bone marrow, a hematopathologist confirms the diagnosis and identifies the CML phase. A hematopathologist is a specialist who studies blood cell diseases by looking at samples of blood and marrow cells and other tissues.
When examining your blood and bone marrow cells, the hematopathologist confirms the CML diagnosis by:
- the presence of the Philadelphia (Ph) chromosome
- the number of cells with the Bcr-Abl oncogene
The hematopathologist uses one or more lab tests such as those below to examine your cells:
- Cytogenetic analysis identifies certain changes in chromosomes and genes. The hematopathologist looks at how your chromosomes are "mapped." The map is called a karyotype. If he or she detects the Philadelphia (Ph) chromosome on the karyotype and other tests show a high white cell count and cancerous characteristics, the CML diagnosis is confirmed.
- Fluorescence in situ hybridization (FISH) is a sensitive test that can detect Bcr-Abl by using fluorescent dyes. A standard cytogenetic analysis can detect the Ph chromosome in about 90 percent of CML patients. Some patients show no evidence of the Ph chromosome during basic cytogenetic testing, but the FISH test may detect the presence of the abnormal Bcr-Abl gene.
- Polymerase chain reaction (PCR) is an even more sensitive test that can detect and measure Bcr-Abl oncogenes not found by FISH. This molecular test can detect a very small number of CML cells, about one abnormal cell in one million cells. A PCR test can be done on cells from blood or marrow.
If you're diagnosed with CML, you'll undergo blood and bone marrow tests during therapy to measure your treatment response.