The chronic myeloproliferative disorders, Polycythemia Vera, Idiopathic Myelofibrosis, Essential Thrombocytosis, share in common origin in a multipotent hematopoietic progenitor cell and overproduction of one or more of the cellular elements of the blood. Polycythemia Vera, the most common of the three disorders, causes the overproduction of red cells, white cells and platelets; in Idiopathic Myelofibrosis, there may be overproduction of white cells or platelets together with anemia and an increase in bone marrow fibrous tissue. In Essential Thrombocytosis, there is an increase in the number of circulating platelets. In all three disorders, blood cell production can also occur outside the bone marrow, leading to enlargement of the spleen and liver. The blood cells overproduced in these disorders are normal in appearance, leading to difficulties in distinguishing them from other types of blood disorders causing an increase in red cells, white cells or platelets. Systemic Mastocytosis is a rare disorder due to overproduction of a white cell subset, the mast cell, that is characterized by skin, bone and organ infiltration by these cells with symptoms due to organ enlargement and dysfunction and release of mast cell inflammatory mediators. The Hypereosinophilic Syndrome is an uncommon disorder characterized by overproduction and organ infiltration by a white cell subset, the eosinophil, with symptoms due to organ enlargement and dysfunction and release of eosinophil inflammatory mediators.

A Hematology Glossary

Red Cells, also known as erythrocytes, carry oxygen from the lungs to the tissues.

White Cells, also known as leukocytes, are responsible for killing any microorganisms that invade the body.

Platelets are small cellular particles produced in the bone marrow by shedding from very large cells called megakaryocytes and serve as the first line of prevention of bleeding when a blood vessel is damaged.

Polycythemia is the term used to designate overproduction of red cells, white cells and platelets.

Erythrocytosis is the term used to designate the overproduction of red cells alone.

Leukocytosis is the term used to designate overproduction of white cells alone.

Thrombocytosis (or thrombocythemia) is the term used to designate overproduction of platelets alone

Myelofibrosis is the term used to designate an increase in the fibrous tissue of the bone marrow. Myelofibrosis is not a primary process but is always caused by another disorder.

Hematopoietic Progenitor Cells are the parent cells in the bone marrow for red cells, white cells and megakaryocytes. The most primitive hematopoietic progenitor cells are multipotent and give rise to the progenitor cells for red cells, white cells and megakaryocytes.

Myeloproliferative Disease is the term used to define a disease arising in a hematopoietic progenitor cell that results in the uncontrolled (autonomous) overproduction of normal-appearing blood cells in the absence of an appropriate stimulus such as lack of oxygen for red cells, lack of microbial invasion or inflammation for white cells and lack of bleeding for platelets.

Idiopathic (or Essential) is a term used to indicate that the cause for a disease process or disorder is unknown

Clonal is a term used to describe diseases arising from a single cell.

Cytogenetics is a technique used to analyze the number and integrity of a cell's chromosomes

Bone Marrow Aspirate is a technique, similar to drawing blood, for obtaining bone marrow for microscopic examination, cytogenetics and flow cytometry.

Bone Marrow Biopsy is a technique by which a piece of bone containing marrow is obtained when marrow cannot be aspirated to identify the presence of myelofibrosis, and to assess marrow cellularity and architecture.

Flow Cytometry is a technique by which individual blood or marrow cells can be analyzed for clonality.

Uric Acid is a by-product of DNA that can accumulate and cause kidney stones or gouty arthritis if the white count is high or if white cells are being rapidly destroyed by chemotherapy.

Phlebotomy is the removal of blood from a vein to reduce the number of red cells and induce iron deficiency to slow their reaccumulation.