Physicians perform a variety of tests to help diagnose leukemia and determine its type and subtype. Diagnostic tests can reveal abnormalities in the appearance of cells and the amounts of different types of blood cells in circulation, changes in the bone marrow, and specific alterations in the genetic and molecular makeup of the diseased cells. These and other factors help in determining the most effective course of treatment.
To help determine specific features of the leukemia cells in the blood or bone marrow, including genetic abnormalities such as chromosomal rearrangements — which are common in ALL — and whether the cells have specific proteins called antigens on their surfaces, physicians perform a number of different tests. The information they learn helps to both identify the cells’ origins and to determine the patient’s prognosis. The 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, which are highly sensitive DNA and RNA tests to determine specific genetic traits of cancer cells
In order to do these studies, physicians need to collect blood and tissue samples. There are several procedures that allow them to obtain these samples.
Blood tests can show whether the amounts of various components of blood are within normal ranges. For example, patients with leukemia may have low numbers of red blood cells, which causes anemia; platelet levels may be low, leading to bleeding and bruising; and white blood cell levels may be diminished, which can lead to frequent infections.
Physicians perform a bone marrow biopsy by inserting a hollow needle into the hip bone to remove a small piece of bone marrow for examination. In a bone marrow aspirate, they withdraw a small sample of liquid bone marrow through a syringe. Doctors use these tests 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 ALL, the number of blasts in the marrow increases to between 30 and 100 percent.
If doctors find diseased cells in the bone marrow, they will also typically perform a lumbar puncture, or spinal tap, to see if leukemia cells are in the fluid that surrounds the brain and spinal cord (cerebrospinal fluid).
Physicians sometimes use imaging tests including chest x-rays, ultrasound, CT scans, MRI, and PET scans to determine whether ALL has affected the bones or organs such as the kidneys or brain, or the lymph nodes.
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 considered experimental.