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Diagnosis of Myelogenous Leukemia


Table of Contents

General Information

A diagnosis is recognition of a disease from its signs and symptoms and the results of laboratory tests.  Occasionally, the physician can diagnose a disease by studying the outward symptoms; however, in order for more complex diseases to be diagnosed, laboratory tests need to be performed. Each disease has various causes and specific laboratory tests which need to be performed in order to gain insight into what the abnormality might be caused by.

Leukemia is a type of cancer that affects the bone marrow, causing increased production of white blood cells which influx the blood stream.  When diagnosing leukemia, laboratory tests must be performed to help the physician to determine which type of leukemia is affecting the patient, either acute myelogenous leukemia, chronic myelogenous leukemia, acute lymphocytic leukemia, or chromic lymphocytic leukemia.  
In order for myelogenous leukemia to be correctly diagnosed, a physician will order a complete blood count, bone marrow biopsy, and cytogenetic tests.1 


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Complete Blood Count (CBC)

When testing for leukemia, one of the first tests that will be performed by a laboratory scientist is a CBC.  The results of a CBC describe all aspects of the blood stream including white blood cell count, red blood cell count, hemoglobin, platelet count, hematocrit, and red blood cell distribution.2  When diagnosing leukemia, the results that are the most important to the diagnosis are the white blood cell count, red blood cell count, and platelet count.  

1.  White Blood Cell Count

A white blood cell count is the total number of white blood cells found in the blood.  A white blood cell usually is helpful since it breaks down foreign matter in the blood that may cause infection or disease.  However, when there is an increase in white blood cells, it is either due to a serious illness or leukemia.  

2.  Red Blood Cell Count

A red blood cell count is the total number of red blood cells found in the blood.  In leukemic patients, the test results should reveal a decrease in the total amount of red blood cells.

3. Hemoglobin

Hemoglobin is the protein found in the red blood cells which carry oxygen to various parts of the body.  Since a leukemia patient has a decreased number of red blood cells, the hemoglobin should also lower than normal.

4. Platelet Count

A platelet count is the total number of platelets found in the blood.  Platelets are used to help clot the blood when the skin is scraped and opened to the outside.  In leukemia patients, the number of platelets should be lower than normal. 

5. Hematocrit

Hematocrit is the volume of space taken up by packed red blood cells, measuring the size and number of the total red blood cells.  The results are shown as a percentage of total red blood cells.  A low hematocrit would signify leukemia.

6. Red Blood Cell Distribution

Red blood cell distribution is the distribution of the widths of the red blood cells found in the blood.  Immature red blood cells are usually larger in size than the mature cells.

Table 1: Example of a Complete Blood Count Test Result
Healthy Patient3 Leukemia Patient3
White Blood Cell Count 4,100-9,000 cells/µL 52,000 cells/µL
Red Blood Cell Count 4.10-5.80 million cells/µL 1.13 million cells/µL
Hemoglobin 12.8-17.2 g/dL 5.1 g/dL
Platelet Count 140,000-350,000 µL 173,000 µL
Hematocrit 20.4% 14.1%
Red Blood Cell Distribution 11.4-14.7% 20.4%
3. Patient test results from http://www.ascls.org/education/CLI/CLI-CaseStudy1-Summer2005.pdf.  
Results are an example and not necessarily the same counts for every leukemia patient


Since leukemia is a disease that involves the white blood cells, the results of a person with leukemia would show an increase in white blood cell count, as seen in Table 1.  In addition, most patients with leukemia will also show a decrease in the number of red blood cells, indicating anemia, and in the number of platelets, indicating thrombocytopenia.  While a CBC cannot accurately diagnose leukemia, it is an important indicator that leukemia is present and additional tests should be ordered to diagnose the type.



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Bone Marrow Aspiration and Biopsy

Bone marrow is found in the hollow interior parts of the flat and long bones.  It contains stem cells and immature red blood cells, white blood cells, and platelets.  The bone marrow is the place where the immature cells remain until they are needed to mature and be released into the blood.

A bone marrow aspiration is when a small amount of bone marrow is removed from the back of the pelvic bone or sternum, while a bone marrow biopsy is when actual pieces of bone are removed in addition to the bone marrow.  This test is helpful since the growth and maturation of the white blood cells begin in the bone marrow, however if leukemic cells are found within the bone marrow in addition to the white blood cells, red blood cells, and platelets, the patient will be diagnosed with leukemia
.4
 This test is always performed when a person is believed to be affected with leukemia since leukemic cells must be found and identified in the bone marrow.

Test results for a healthy patient would show normal counts of red blood cells, white blood cells, and platelets in the bone marrow, while the test results for a leukemia patient would show leukemic cells in the bone marrow.




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Cytogenetic Tests

Cytogenetic tests are tests that are performed in order to understand the genetic aspect of the leukemia cells.  In myelogenous leukemia, cytogenetic testing is used for identifying the bcr-abl gene and the presence of the Philadelphia chromosome on the leukemic cells.  The Philadelphia chromosome is a translocation (or rearrangement) of the arms of chromosomes 9 and 22 resulting in a shortened chromosome 22.  This translocation occurs in more than 90% of CML patients.5  There are two types of cytogenetic tests performed for myelogenous leukemia diagnosis, fluorescent in situ hybridization and polymerase chain reaction.

1. Fluorescent in situ Hybridization (FISH)
FISH is performed using blood or the bone marrow collected from a bone marrow aspiration.  A cytologist will test the cells by using a fluorescent dye that can attach to only leukemic cells, specifically the bcr-abl gene on the chromosome of the cell.  The leukemic cells will be a different color when viewing the cells through a microscope.  This test is extremely accurate when it comes to diagnosing the cancer cells.

2. Polymerase Chain Reaction (PCR)
PCR is another DNA test that identifies the bcr-abl gene on the leukemic cell using the blood or bone marrow.  This test is capable of finding the translocations on the cell that are too small to be viewed through a microscope.



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References:
  1. American Cancer Society.  How is Chronic Myeloid Leukemia (CML) Diagnosed?  ACS Web Site.  Available at: http://www.cancer.org/docroot/CRI/content/CRI_2_4_3x_How_Is_Chronic_Myeloid_Leukemia_CML_Diagnosed.asp?sitearea=.  Accessed April 16, 2008.
  2. Lab Tests On line.  Complete Blood Count.  Lab Tests On line Web Site.  Available at: http://www.labtestsonline.org/understanding/analytes/cbc/test.html. Accessed April 6, 2008.

  3. American Society for Clinical Laboratory Science. Clinical Lab Investigations: Case Studies for the Laboratory Professional.  ASCLS Web Site.  Available at: http://www.ascls.org/education/CLI/CLI-CaseStudy1-Summer2005.pdf.  Accessed April 16, 2008.

  4. National Heart, Lung, and Blood Institute.  Bone Marrow Tests. HNLBI Web Site.  Available at: http://www.nhlbi.nih.gov/health/dci/Diseases/bmt/bmt_all.html.  Accessed April 6, 2008.

  5. Hooberman AL, Carrino JJ, Leibowitz D, et al. Unexpected heterogeneity of BCR-ABL fusion mRNA detected by polymerase chain reaction in philadelphia chromosome-positive acute lymphoblastic leukemia. Proc Natl Acad Sci U S A. 1989;86:4259-4263. Available from: http://www.jstor.org/stable/33665.


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This website was created by Kathleen Schieffer, a medical technology student at the University of Delaware, for a class project.  The purpose is to give the public eye insight into the laboratory diagnosis of leukemia.

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Last Updated: May 12, 2008
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