Physicians perform an array of tests to diagnose chronic myelogenous leukemia (CML). The three main tests doctors use are blood tests, bone marrow aspirates/biopsies, and genetic testing for the Philadelphia chromosome.
Blood tests can show whether the numbers of various components of your blood are within the normal range. Doctors perform a complete blood count to detect abnormalities in your levels of white cells, which fight infection; red cells, which carry oxygen; and platelets, which are crucial to blood clotting.
Bone Marrow Aspirates & Biopsies
Doctors typically test the bone marrow to determine if a person has CML and to monitor a patient's response to treatment. These tests — bone marrow aspirate and biopsy — are the cornerstone of diagnosing and monitoring CML.
During a bone marrow aspirate, the patient lies on his or her stomach. The skin above the hip bone (called the iliac crest) is cleaned and numbed with novocaine. A very thin needle is then inserted into the hip bone and small particles are removed and sent for testing.
A biopsy can be performed at the same time, using a separate needle to remove a core of bone.
Doctors examine bone marrow and blood samples using standard genetic tests called karyotyping, FISH (fluorescence in situ hybridization), and PCR (polymerase chain reaction).
- Karyotyping examines the bone marrow for the appearance of Philadelphia chromosomes in dividing cells. This technique can show structural changes in the chromosomes.
- FISH is used to determine the percentage of cells with the BCR/ABL fusion gene.
- PCR is a laboratory method used to make many copies of a specific DNA sequence, and is the most sensitive method for detecting the presence of diseased cells.
FISH and PCR tests can be conducted using peripheral blood (blood circulating in the body).
Once these tests are complete, your physician can determine how advanced your disease has become. CML is divided into three phases. Knowing what phase the disease has reached helps guide your physicians as they plan your treatment.
During this earliest stage of the disease, patients have a low number of blasts, or immature cells, within the bone marrow. In this phase blasts make up less than 5 percent of all bone marrow cells. Symptoms in the chronic phase are often mild. Most CML patients are diagnosed during this phase.
In the accelerated phase, the number of blasts rises to between 5 and 19 percent of all bone marrow cells. Patients may develop symptoms including fever, weight loss, and a decrease in appetite because the spleen is enlarged.
When the number of blasts increases to more than 20 percent of bone marrow cells, patients are considered to be in the blast phase, sometimes called a blast crisis. This phase of the disease is difficult to treat.
Doctors also distinguish among these phases of CML by determining if a patient has chromosomal abnormalities in addition to the Philadelphia chromosome. For example, if a patient has two Philadelphia chromosomes the disease is usually diagnosed as accelerated phase disease even if the blast count is less than 5 percent.