Myeloproliferative disorders are a group of diseases in which the bone marrow produces too many red blood cells, white blood cells, or platelets.

Normally, the bone marrow makes stem cells (immature blood cells) that develop into mature blood cells. There are 3 types of mature blood cells:

• Red blood cells that carry oxygen and other materials to all tissues of the body.
• White blood cells that fight infection and disease.
• Platelets that help prevent bleeding by causing blood clots to form.

Myeloproliferative disorders begin in the bone marrow and may cause a greater than normal number of stem cells to develop into one or more types of blood cells. The disorders usually get worse slowly as the number of extra blood cells slowly increases.

There are 6 types of chronic myeloproliferative disorders.

The type of myeloproliferative disorder is based on whether too many red blood cells, white blood cells, or platelets are being made. Sometimes the body will make too many of more than one type of blood cell, but usually one type of blood cell is affected more than the others are. Chronic myeloproliferative disorders include the following 6 types:

• Chronic myelogenous leukemia.
• Polycythemia vera.
• Chronic idiopathic myelofibrosis.
• Essential thrombocythemia.
• Chronic neutrophilic leukemia.
• Chronic eosinophilic leukemia.

These types are described below. Chronic myeloproliferative disorders sometimes become acute leukemia, in which too many abnormal white blood cells are made.

Tests that examine the blood and bone marrow are used to detect (find) and diagnose chronic myeloproliferative disorders.

The following tests and procedures may be used:

• Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient’s health habits and past illnesses and treatments will also be taken.
• Complete blood count (CBC) with differential: A procedure in which a sample of blood is drawn and checked for the following:
  • The number of red blood cells and platelets.
  • The number and type of white blood cells.
  • The amount of hemoglobin (the protein that carries oxygen) in the red blood cells.
  • The portion of the blood sample made up of red blood cells.
  
  
  Complete blood count (CBC). Blood is collected by inserting a needle into a vein and allowing the blood to flow into a tube. The blood sample is sent to the laboratory and the red blood cells, white blood cells, and platelets are counted. The CBC is used to test for, diagnose, and monitor many different conditions.
• Bone marrow aspiration and biopsy: The removal of bone marrow, blood, and a small piece of bone by inserting a hollow needle into the hipbone or breastbone. A pathologist views the bone marrow, blood, and bone under a microscope to look for signs of cancer.
• Cytogenetic analysis: A test in which cells in a sample of blood or bone marrow are viewed under a microscope to look for certain changes in the chromosomes. Certain diseases or disorders may be diagnosed or ruled out based on the chromosomal changes.