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. 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. Tests your doctor may use to diagnose and monitor your CML are outlined, below.
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
If you're diagnosed with CML, you'll undergo blood and bone marrow tests during therapy to measure your treatment response.
Tests your doctor may use to diagnose CML:
- Blood tests
- Bone marrow tests
- Cytogenetic analysis
- Fluorescence in situ hybridization (FISH)
- Polymerase chain reaction (PCR)
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 usually don't have these blast cells, promyelocytes and myelocytes in their blood.)
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
This test 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.
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)
This test is used to diagnose CML and to track response to therapy once treatment has begun. This test can be performed with either blood or bone marrow cells. It is an extra-sensitive test that can detect and measure BCR-ABL oncogenes not found by other tests, such as FISH. PCR allows more sensitive follow-up of patients in remission and can help determine whether additional treatment is needed. For detailed information, access the free information booklet, Chronic Myeloid Leukemia.
How often should CML patients receive PCR testing?
PCR testing is generally performed at diagnosis and every three months after initiation of therapy.
How do CML patients access PCR testing?
The patient’s doctor can send the patient’s blood sample for BCR-ABL PCR testing (which requires specialized equipment and expertise) to
- A reference laboratory (used for specialized tests that are ordered only occasionally or require specialized equipment)
- An academic center
- An NCI (National Cancer Institute) center laboratory.
See what doctors and patients say about the value of PCR testing: