It is essential to accurately diagnose a patient’s specific type of leukemia, as treatments depend on which type is involved. Many tests are used to establish a leukemia diagnosis.
Complete blood count
This basic test obtains an accurate count of all the different types of blood cells. The hallmark of leukemia is an overabundance of white blood cells (leukocytes), and in some cases, this may be the first sign that alerts the doctor to the presence of leukemia. In chronic lymphocytic leukemia, characteristic cells called smudge cells (cells that rupture in the preparation of the blood smear) appear in significant numbers.
Bone marrow aspirate and biopsy
In this test, a needle is inserted into the hipbone or the sternum to obtain a small piece of bone and sample of bone marrow. A pathologist examines the samples under a microscope to classify the leukemia according to cell type and other parameters.
Lumbar puncture (spinal tap)
In some types of leukemia, doctors need to look for leukemia cells in cerebrospinal fluid surrounding the brain and spinal cord. After part of the lower back is numbed, some of the spinal cord fluid is withdrawn using a needle, and examined microscopically.
Cytochemistry and immunocytochemistry
Cytochemistry refers to using special stains and chemical reactions to differentiate between types of leukemia. Immunocytochemistry uses the same principle, employing antibodies to produce distinct color changes in the cell sample that allow the pathologist to identify the type of leukemia present.
Immunophenotyping classifies cells according to their immunologic characteristics. This test uses monoclonal antibodies to more accurately determine the type of leukemia. The presence or absence of certain antigens, called CD antigens, cell surface markers expressed by leukocytes, is very useful in determining cell lineage (whether the leukemia derives from T cells or B cells), as well as in predicting whether the leukemia is likely to take an indolent or aggressive course. This is invaluable in devising treatment strategy.
Cytogenetics (chromosome analysis)
Since some leukemias, such as chronic myelogenous leukemia and acute myeloid leukemia, are caused by chromosomal translocations, getting a complete chromosome analysis may provide important diagnostic information.
Molecular testing, including polymerase chain reaction testing
This test examines genes in the leukemia cell. The presence of certain genes, called oncogenes, can help diagnose precisely what form of leukemia is present. For example, in chronic myelogenous leukemia, an oncogene called bcr-abl is often the determining factor in making a diagnosis.