Leukemia

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Diagnosis

Once the physician suspects that a patient's blood is abnormal, blood and bone marrow tests are performed to rule out leukemia. Additional tissue samples may be needed to confirm the diagnosis or to help plan treatment.

Blood Tests
To diagnose leukemia, a number of blood tests are performed. These tests are used to evaluate the type and quantity of blood cells that are present, the blood chemistry, and other factors.

Full blood count—Full blood count is used to establish the numbers of different blood cell types within the circulation. Low numbers of red or white blood cells are described as anemia or leukopenia, respectively. Low numbers of "young" red blood cells (reticulocytes) are described as reticulocytopenia. High leukocyte or reticulocyte counts are called leukocytosis or reticulocytosis, respectively. A lack of mature neutrophils (bacteria-destroying white blood cells) is known as neutropenia or granulocytopenia. Thrombocytopenia is the term used for a low number of blood-clotting platelets, and thrombocytosis refers to a high number of platelets.

Differential blood count—Differential blood count is used to determine the relative proportion of blood cell types within the bloodstream. In particular, the percentage of immature leukemic "blast" cells is noted. People with acute leukemia (either acute lymphocytic leukemia [ALL] or acute myelogenous leukemia [AML]) often have too many leukocytes (white blood cells), too few erythrocytes (red blood cells) and/or too few platelets. Often many of the leukocytes in these individuals are immature "blast" cells.

Hematocrit assay—Hematocrit assay is used to determine the proportion of the blood that is occupied by erythrocytes (red blood cells); normal men: 46% (39.8 - 52.2); normal women: 40.9% (34.9 - 46.9).

Hemoglobin level —Hemoglobin level is used to evaluate the amount of oxygen-carrying pigment in the erythrocytes; normal men: 15.5 g/dl blood (13.3 - 17.7); normal women: 13.7 g/dl blood (11.7 - 15.7).

Blood coagulation—Blood coagulation variables are used to determine whether there are problems with clotting. Such variables include prothrombin time, partial prothrombin time (PPT), clotting time, coagulation factors II, V, VII, IX, X, XI, and XII, plasminogen, and plasminogen activator.

Blood morphology and staining—Blood morphology and staining is used to identify abnormalities in cell shape, structure, and the condition of the cell nucleus. Some abnormalities common to red blood cells include anisocytosis (excessive variations in size), poikilocytosis (abnormal red blood cell shapes), and macrocytosis (abnormally large cells). Neutrophils often show nuclear and cell-based abnormalities, as well as loss of granulation. Platelets may show giant forms that are deficient in granules.

Blood chemistry—Blood chemistry is used to measure the type and amount of enzymes, minerals, and other substances within the blood. Typical tests include measuring the serum enzyme lactic dehydrogenase; measuring the leukocyte enzyme alkaline phophatase, especially for the diagnosis of chronic myelogenous leukemia, or CML; measuring serum vitamin B12, which can be increased to roughly 15 times normal in CML patients; and measuring serum levels of calcium, potassium, phosphate, and uric acid (excess uric acid in the blood, or hyperuricemia, is common in lymphocytic leukemia and lymphoma). These tests are used to identify kidney or liver damage that may be caused by leukemic cell breakdown or by drugs used for chemotherapy.

Bone Marrow Tests
The bone marrow is sampled by a technique known as bone marrow aspiration. During this procedure, a thin hollow needle with a syringe attachment is used to suction up (aspirate) a teaspoon-sized sample of liquid bone marrow from the back of the hip bone. A larger needle then is employed to obtain a bone marrow biopsy ("core" biopsy), which removes roughly a 1/16 inch cylindrical piece of bone marrow from the hip site. After the bone marrow samples are obtained, they are examined by many physician specialists, including a pathologist (disease diagnosis specialist, who examines samples under a microscope), hematologist (blood specialist), and oncologist (cancer specialist).

Microscopic examination—Microscopic examaination is performed on samples of the bone marrow, as well as any samples of the blood, cerebrospinal fluid, or lymph node tissue. The bone marrow cells are evaluated according to their size, shape, and content of granules (cellular enzymes that help some leukocytes to destroy germs).

Then they are classified with respect to maturity:

1. Mature cells are normal cells of the circulating blood, which are functional infection-fighters that can no longer reproduce.
2. Immature cells are undeveloped blood cells that, although poor infection-fighters, are still able to reproduce.
3. Blast cells are the most immature form of bone marrow cells.

The samples also are categorized according to their number of cells (cellularity), because abnormal tissue may contain appropriate proportions of blood-forming (hematopoietic) versus fat cells. Hypercellular marrow holds too many hematopoietic cells, whereas hypocellular marrow holds too few hematopoietic cells.

Cytochemistry—Identification of the chemical components of cells is conducted to distinguish different types of leukemia. Cytochemical tests often use special colored dyes (stains) that are only visible under a microscope. For example, one stain turns the granules of most acute myelogenous leukemia (AML) cells black, although acute lymphocytic leukemia (ALL) cells are unaffected by this substance. Leukocyte alkaline phosphate (LAP) or neutrophil alkaline phophatase (NAP) tests formerly have been used to distinguish CML from other types of leukemia and noncancerous blood disorders; however, these assays no longer are considered particularly helpful in diagnosis, except in the absence of cytogenetic (cell genetic material) or other studies.

Flow cytometry—Flow cytometry is a computer-assisted technique in which bone marrow or other cells are treated with special antibodies and then are placed in front of a laser beam. Some types of leukemia cells contain special binding molecules called receptors that cause the antibodies to "label" (stick to) them. Laser treatment makes the antibody-coated cells fluorescent. The light that is given off undergoes computer measurement and analysis. The leukemia cells are counted and categorized by this method.

Immunocytochemistry—Immunocytochemistry, like flow cytometry, uses antibodies to treat the bone marrow or biopsy samples. Yet unlike flow cytometry, computers and lasers are not needed for this procedure. Instead, the sample is prepared so that specific types of cells undergo a color change that can be identified under a microscope. Immunocytochemistry allows the pathologist to identify specific types of leukemia.

Cytogenetic studies—Cytogenetic studies employ a variety of techniques for cell culture, slide-making, and preparation of chromosomes (genetic material). Bone marrow aspirate is the preferred tissue for most blood disorders; however, if unavailable, blood samples may be used if there are enough circulating blast cells. In cases of chronic lymphocytic leukemia (CLL), blood samples are essential; in lymphoma cases, lymph node samples will provide more information.

Researchers have found that leukemia cells often contain genetic defects known as translocations, inversions, deletions, and additions. Translocations are genetic errors that result when parts of two chromosomes are exchanged. Inversions are produced when part of a chromosome becomes inverted (upside down) and the order of its genetic material is reversed. Deletions occur when part of a chromosome is missing, and additions are caused by duplications of all or part of a chromosome.

Chronic myelogenous leukemia (CML)— CML was the first type of cancer to show a consistent cytogenetic abnormality. This abnormality—a translocation between chromosomes 9 and 22 (written as t [9;22])—is known as the Philadelphia chromosome (Ph1). The Philadelphia chromosome causes uncontrolled reproduction and proliferation of all types of white blood cells and platelets.

Immunophenotyping—Immunophenotyping is the classification of cell types according to their immunologic characteristics. With the development of a form of testing known as monoclonal antibody (MAb) technology, types of leukemia cell lines are now better defined. Numerous antibody reagants have been identified; reagents are substances used to create chemical reactions. Some reagants recognize specific "clusters of differentiation" (CD); for example, CD79 recognizes B-cells, CD3 recognizes T-cells, and antimyeloperoxidase recognizes myeloid cells. Other useful, but less specific reagants are CD19, CD22,CD5, CD7, CD13, CD33, glycophorin, and CD61.

Imaging Studies
Imaging studies may be used to determine whether the leukemia has invaded other organs within the body.

Such studies include:

• X-rays to see whether there are enlarged lymph nodes in the chest, a localized mass in the lungs, or evidence of spread to the outer bones or joints.
• Computed tomography (CT or CAT) scan is a computer-assisted x-ray that produces cross-sectional images of the body. CT scans are not often used in leukemia patients unless the physician suspects that the disease has spread. In such cases, CT scans may detect changes in the lymph nodes around the heart, trachea (windpipe), or abdomen. Lymph node enlargement is more common in patients with acute or chronic lymphocytic leukemia (ALL, CLL).
• Magnetic resonance imaging (MRI) scan is a procedure that uses electromagnets and radio waves to create computer-generated pictures of the internal organs. MRI may be used if the physician suspects that leukemia involves the brain or lungs.
• Radionuclide (radioactive atom) scanning may be performed to rule out nonleukemic disorders in patients who complain of bone pain. The radiologist injects the patient with a radioactive chemical (e.g., gallium-67), which will accumulate in areas of infection or malignancy and can be viewed with a special camera. This procedure is not used for patients who already have been diagnosed with leukemia.
• Ultrasound is an imaging method based on the principle that solids reflect sound waves in a manner that can be converted into a picture. During ultrasound, a transducer "probe" releases high-frequency sound waves that bounce off the internal organs, are collected, and are transmitted onto a video screen to create a picture called a sonogram. Ultrasound may be conducted to check the kidneys for leukemia-related damage.

Leukemia, Diagnosis reprinted with permission from oncologychannel.com
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