An accurate diagnosis of the type of leukemia is important. The exact diagnosis helps the doctor to
- Estimate how the disease will progress
- Determine the appropriate treatment.
Diagnosing acute myeloid leukemia (AML) and the AML subtype usually involves a series of tests. Some of these tests may be repeated during and after therapy to measure the effects of treatment.
Tests Used to Diagnose AML
Blood and bone marrow tests are used to diagnose AML and the AML subtype. A change in the number and appearance of blood cells helps to make the diagnosis.
Blood samples are generally taken from a vein in the arm. The blood sample is sent to a lab for testing.
- Complete Blood Count (CBC) with Differential: Measures the number of red blood cells, white blood cells and platelets. Children with AML often have a high number of white blood cells, but most of these are leukemic blast cells that do not protect against infection. They also usually have a low number of red blood cells and platelets.
- Peripheral Blood Smear: Examines the number, shape and size of the blood cells and determines whether there are leukemia (blast) cells in it.
Even if blood test results suggest that your child has leukemia, an AML diagnosis is usually made only after the examination of the bone marrow cells.
Bone Marrow Tests
Samples of marrow cells are obtained by bone marrow aspiration and biopsy. Bone marrow testing involves two steps usually performed 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.
Bone marrow samples are usually taken from the hip bone. Both samples are examined under a microscope to look for chromosomal and other cell changes.
AML cells can spread to the cerebrospinal fluid, the fluid that flows around the brain and spinal cord. After the area over the spine in the lower part of the back has been numbed with local anesthesia, a thin needle is inserted between two vertebrae (back bones) and into the cerebrospinal fluid. The sample is sent to a lab for testing.
Blood, bone marrow and cerebrospinal fluid samples are examined under a microscope to determine if the cells look like normal, mature blood cells or abnormal, immature blood cells (blast cells).
Typically, there are no blast cells in the blood, and no more than 5% of the cells in the bone marrow are blast cells. A diagnosis of AML generally requires a finding of 20% or more of the cells in the bone marrow sample to be myeloid blast cells.
Immunophenotyping (Flow Cytometry)
A flow cytometry test can measure the number of cells in a sample, as well as specific characteristics of the cells, including their size and shape, and identify specific markers on the cell surface. Leukemia cells can have different antigens on their surfaces, depending on the type of leukemia. In addition to its use as a diagnostic test, flow cytometry is also used after treatment for evaluating minimal/measurable residual disease (MRD). This refers to the small number of cancer cells that may remain in the body after treatment.
Genetic tests help identify changes (mutations) in the genes or chromosomes of a cell. Identifying these specific changes can help determine the patient's treatment options and prognosis. The following tests may be done to examine the genes of a patient's leukemia cells:
- Cytogenetic analysis (karyotyping)
- Fluorescence in situ hybridization (FISH)
- Polymerase chain reaction (PCR)
- Next-generation sequencing
Genetic testing should be done when the cancer is first diagnosed and may also be indicated after a relapse. This is because it is possible for patients to acquire additional genetic abnormalities after the completion of their initial, “first-line” treatment.
Before your child starts treatment for AML, tests will be done to learn more about your child’s overall health. Tests may include:
- Blood chemistry profile
- Human leukocyte antigen (HLA) typing
- Download or order LLS's free booklets:
- Caring for Kids and Adolescents with Blood Cancer: A Workbook for Families
- Childhood Blood Cancer
- Blood Tests
- Understanding Blood Counts
- Bone Marrow Tests