A number of laboratory tests may be used to help diagnose leukemia, determine the type, and monitor the effectiveness of treatment. After successful treatment (remission), testing may be use to monitor for recurrence of disease.
- Complete blood count (CBC) and WBC differential. These routine tests are ordered to count the number, maturity, and proportion of different types of cells in the blood. These tests can provide the first evidence of leukemia, and they are often the first tests ordered to diagnose leukemia. Irregularities in cell counts, such as elevated white blood cell counts or low red blood cell counts, may be due to leukemia or to a variety of temporary or chronic conditions. But blasts (immature blood cell precursors) are not normally seen in the blood, so if they are present, some kind of leukemia is likely and follow-up testing will be ordered. The CBC and differential are also important tools to monitor the effectiveness of treatment and to detect disease recurrence.
- Blood smear. A blood smear, or peripheral blood smear, is often used to follow up a CBC with abnormal white blood cells, red blood cells or platelets, or with unclear results. A drop of blood is smeared on a microscope slide and examined for immature cells or cells with abnormal sizes, shapes or appearance compared to normal cells.
- Bone marrow aspiration/biopsy. Bone marrow is a matrix of fibrous supporting tissue, fluid ("liquid marrow"), undifferentiated stem cells, and a mixture of blasts, maturing and mature blood cells. If a health practitioner suspects that someone has leukemia, a bone marrow aspiration and/or biopsy procedure will be done to look at the fluid and/or tissue in the marrow. In an aspiration, a bone marrow sample is collected from the hipbone, or sometimes the sternum in adults, or the shinbone in infants. A pathologist or other specialist then examines the marrow sample (bone and/or fluid) under the microscope, evaluating the number, size, and appearance of each of the cell types as well as the proportions of mature and immature cells. If leukemia is present, the type and severity of the disease can be determined. This test will also help establish a baseline for bone marrow cells, to see how they respond to treatment.
- Spinal tap (lumbar puncture) and cerebrospinal fluid analysis. If leukemia is found in the bone marrow, a spinal tap may also be done to look for leukemia cells in the cerebrospinal fluid (CSF). If leukemic cells are seen in the CSF, additional treatment (for example, direct injection of drug into the CSF space) may be necessary.
- Immunophenotyping or phenotyping by flow cytometry. This test can be used to help diagnose leukemia and to determine which type of leukemia a person has. Cells from the blood, bone marrow, or lymph nodes are incubated with commercially generated antibodies, which selectively bind to antigens on the surface of leukemia cells or in their cytoplasm. The antigens act like markers and are detected by flow cytometry, a type of test that uses a laser beam and a computer to identify cells types based on the antigens present. This process is known as immunophenotyping and helps to categorize the type of leukemia present.
- Cytogenetic tests (FISH and karyotyping). Cytogenetic tests look at chromosome structure and number. They are used to find abnormal chromosomes associated with leukemias, other cancers, and genetic disorders. They help diagnosis and differentiate leukemias by detecting translocations (where part of a chromosome breaks and reattaches to a different chromosome) for certain acute myeloid leukemias, acute promyelocytic leukemias, chronic myelocytic leukemias, and acute lymphoblastic leukemias, among others. These techniques can also detect deletions associated with acute myeloid leukemia or myelodysplastic syndromes and increases or decreases in the number of chromosomes, such as trisomies (trisomy 12) for chronic lymphocytic leukemia.
- Chromosome analysis (karyotyping) is a cytogenetic test that maps the 46 chromosomes in cells to look for changes in arrangement, size, or number (including deletions or translocations) that are associated with leukemia.
- Fluorescent in situ hybridization (FISH) is a cytogenetic test that looks for changes in chromosomes that come from genetic variations. It is generally more sensitive than karyotyping. In FISH, an abnormal gene segment in a chromosome is made to "light up" or fluoresce when it is bound by a special probe. FISH helps diagnose different leukemias that may look similar but have different genetic abnormalities and therefore may require different treatment. For more on this, see the article The Universe of Genetic Testing: Cytogenetics (Chromosome Analysis).
- Polymerase chain reaction (PCR). One factor that contributes to the uncontrolled growth of cancer cells is malfunctioning proteins that control cell growth and development. Those malfunctions can result from abnormalities in DNA from mutations, inversions, fusions, or deletions of parts of the genetic code. The polymerase chain reaction is a laboratory method that amplifies DNA to detect those abnormalities associated with certain types of leukemia. PCR tests can help guide the type or intensity of treatment and/or determine prognosis for a certain leukemia and sometimes identify the target for therapy (targeted therapy) based on the genetic makeup of the cancer cells. Some common PCR tests and their associated leukemia types are:
- Minimum residual disease (MRD) tests. These are relatively new, more sensitive flow cytometry or PCR-based tests to detect very small amounts of leukemic cells post-treatment, known as minimum residual disease (MRD). This can help guide treatment and prevent relapses after the leukemia has gone into remission.
Computerized tomography (CT), magnetic resonance imaging (MRI), chest x-rays, or positron emission tomography (PET) scans are sometimes used to look for signs of the disease (tumors and masses of cells) in areas such as the chest. Other imaging scans, like ultrasound, may also be used to evaluate the status of body organs such as the spleen, liver, and kidney.
For more on these, see the web site RadiologyInfo: The radiology information resource for patients.