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Diagnosing acute lymphoblastic leukemia (ALL) and the ALL subtype usually involves a series of tests. An accurate diagnosis of the subtype is important. The exact diagnosis helps the doctor

  • Estimate how the disease will progress
  • Determine the appropriate treatment

In children, a diagnosis of ALL generally requires a finding that 25 percent or more of the cells in the bone marrow are leukemic blasts of lymphoid origin (lymphoblasts).

Some of the tests used to diagnosis ALL may be repeated both during and after your child’s treatment to evaluate if treatment is working.

Blood and Bone Marrow Tests

Complete Blood Count (CBC) with Differential. This test is used to measure the number of red blood cells, white blood cells and platelets in a sample of blood. It measures the amount of hemoglobin in the red blood cells. The CBC should include a differential. The differential measures the numbers of the different types of white blood cells in the sample.

Children with ALL often have a high number of white blood cells, but most of these are leukemia cells that do not protect against infection. Meanwhile, they may not have enough mature white blood cells, red blood cells or platelets.

Even if the CBC findings suggest leukemia, an ALL diagnosis is usually only made after examination of a sample of bone marrow cells.

Bone Marrow Aspiration and Biopsy. These two procedures are generally done at the same time in a doctor's office or a hospital. Most children are under sedation or general anesthesia during these procedures. The samples are usually taken from the hip bone using specialized needles.

  • A bone marrow aspiration removes a liquid marrow sample
  • A bone marrow biopsy removes a small amount of bone filled with marrow

Cell Assessment. A hematopathologist will examine a sample of blood cells or bone marrow cells under the microscope to determine the size, shape, and type of cells as well as to identify other features of the cells. A significant finding is the appearance of the cells—whether the cells look more like normal, mature blood cells or more like abnormal, immature blood cells (blast cells).

The percentage of blast cells identified in the samples is another important finding. Typically, there are no blast cells in the blood, and no more than 5 percent of the cells in the bone marrow are blast cells. Generally, a diagnosis of ALL in children requires a finding of 25 percent or more of the cells in the bone marrow to be lymphoblasts.

Flow Cytometry. This laboratory test can detect specific types of cancer cells based on the antigens or proteins on the surface of the cells. The pattern of the surface proteins is called the “immunophenotype.” It is used to help diagnose specific types of leukemia and lymphoma cells.

A bone marrow sample is often used for this test, but it can also be done with a blood sample.

Depending on the type of leukemia, the leukemia cells can have different antigens on their surfaces that can be helpful in identifying leukemia cells.

Flow cytometry helps to confirm an ALL diagnosis. It is also used to determine the type of lymphocytes (B cells or T cells) in which the disease originated and to assess the maturity of the cells.

Genetic Tests

The following tests are used to identify, examine and measure chromosomes and genes.

Cytogenetic Analysis. In this test a hematopathologist uses a microscope to examine the chromosomes inside of cells. Cytogenetic analysis is used to look for abnormal changes in the chromosomes of the leukemia cells of patients with ALL.

Cytogenetic testing is done using either a bone marrow or a blood sample to search for any abnormal changes in the size, shape, structure or number of chromosomes in the leukemia cells.

Cytogenetic analysis provides information that is important when determining a patient’s treatment options and prognosis. This information can predict how the disease will respond to therapy.

For example, a translocation between chromosomes 9 and 22 is associated with a diagnosis of Philadelphia chromosome-positive (Ph+) ALL, a subtype of ALL that is treated differently than other subtypes.

Fluorescence in situ Hybridization (FISH). This is a cytogenetic laboratory technique that is used to identify and examine genes or chromosomes in cells and tissues. In cases of ALL, doctors use FISH to detect certain abnormal changes in the chromosomes and genes of leukemia cells.

Polymerase Chain Reaction (PCR). A PCR is a very sensitive laboratory technique that is used to detect and measure some genetic mutations and chromosomal changes that are too small to be seen with a microscope. Polymerase chain reaction testing essentially increases or “amplifies” small amounts of specific pieces of either RNA (ribonucleic acid) or DNA to make them easier to detect and measure. This test can find a single leukemia cell among more than 500,000 to one million normal cells. Polymerase chain reaction testing is one method used to determine the amount of minimal residual disease (MRD), the small amount of cancer cells left in the body after treatment. This testing can be done on a bone marrow or a blood sample.

Next-generation sequencing. This technique refers to several different laboratory tests that can rapidly examine the exact sequence (order) of DNA or RNA. This makes it possible to identify a variety of genetic alterations in a patient’s cancer cells. These alterations are important in guiding risk assessment and prognosis, and may also guide treatment decisions.

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