Physicians perform an array of tests to help diagnose leukemia and determine both its type and specific subtype. The tests can uncover abnormalities in the amounts of different kinds of circulating blood cells, changes in the cellular makeup of the bone marrow, alterations in the genetic and molecular makeup of the diseased cells, and other factors that are helpful in deciding on the most effective course of treatment.
Blood tests can show whether the amounts of various components of blood are within normal ranges. In patients with AML, red blood cell levels may be low, causing anemia; platelet levels may be low, which can cause bleeding and bruising; and normal white blood cell levels may be diminished, leading to infections.
Doctors examine bone marrow to determine the number of blasts, or immature cells, in the marrow and to reveal other features of the leukemic cells. Normally, blasts account for less than 5 percent of bone marrow content. In patients with leukemia, blasts increase to more than 20 percent of marrow. In a bone marrow biopsy, physicians use a hollow needle inserted into the hip bone to remove a piece of marrow and bone for examination. In a bone marrow aspirate, a small sample of liquid bone marrow is withdrawn using a syringe.
It may also be necessary for physicians to perform a lumbar puncture, or spinal tap, in which they take a sample of cerebrospinal fluid, the fluid that surrounds the brain and spinal cord (the central nervous system, or CNS), to see if the disease has spread there.
In addition, physicians use a number of tests that help them determine specific features of the leukemia cells in the blood or bone marrow, including genetic abnormalities such as chromosomal rearrangements — which are common in leukemias — and whether the cells have specific proteins called antigens on their surfaces. This information helps both identify the cells’ origins and to determine the patient’s prognosis. These tests include the following:
- cytogenetic studies to determine chromosomal changes in cells
- immunohistochemistry studies, in which antibodies are used to distinguish between types of cancer cells
- flow cytometry, in which prepared cells are passed through a laser beam for analysis
- molecular genetic studies, in which highly sensitive DNA and RNA tests are used to determine specific genetic traits of cancer cells
Physicians sometimes use imaging tests to determine whether AML has affected the bones or organs such as the kidneys or brain, or the lymph nodes. These tests can include chest x-rays, ultrasound, computed tomography (CT) scan, and magnetic resonance imaging (MRI).
New diagnostic tests and procedures are emerging from work on the human genome and gene expression analysis, and these are likely to be important in the future but are currently experimental.