Polycythemia
Visual Explanation: http://www.youtube.com/watch?v=E8QzQHD9WPg&list=PLZ3IB-GR0QfCIuneZcxpIEPCs4e-iRxMg&index=2
Background Information
Polycythemia is a medical condition in which the proportion of blood volume that is occupied by red blood cells increases. Blood volume proportions can be measured as hematocrit level and can be due to two factors; Absolute and Relative Polycythemia, which will be further discussed below. Polycythemia is occasionally termed erythrocytosis,
but the terms are not synonymous because polycythemia refers to any
increase in red blood cells, whereas erythrocytosis only refers to a
documented increase of red cell mass.
The emergency treatment of polycythemia (e.g., in hyper-viscosity or thrombosis) is by venesection,
the removal of blood from the circulation. Depending on the underlying
cause, venesection may also be used on a regular basis to reduce the RBC count. Cytostatics (busulfan, hydroxyurea) are sometimes used if venesection is ineffective or contraindicated.
Types of Polycythemia
1. Relative Polycythemia
Relative polycythemia is an apparent increased in the erythrocyte level in the blood; though, the underlying cause is reduced concentration of blood plasma. Relative polycythemia is often caused by excessive lost of body fluids due to burns, dehydration and stress. A specific type of relative polycythemia is Gaisböck syndrome. In this syndrome, primarily occurring in obese men, hypertension causes a reduction in plasma volume, resulting in (amongst other changes) a relative increase in red blood cell count
2. Absolute Polycythemia
Absolute polycythemia is defined by the overproduction of RBCs due to a primary process in the bone marrow (a so-called myeloproliferative syndrome), or may be a reaction to chronically low oxygen levels or, rarely, a malignancy. Alternatively, additional RBCs may have been received through another process—for example, being over-transfused (either accidentally or, as blood doping, deliberately) or being the recipient twin in a pregnancy, undergoing twin-to-twin transfusion syndrome.
A) Primary Polycythemia
Primary polycythemias are due to factors intrinsic to red cell precursors. Polycythemia vera (PCV), polycythemia rubra vera (PRV), or erythremia, occurs when excess red blood cells are produced as a result of an abnormality of the bone marrow. Often, excess WBCs and platelets are also produced. Polycythemia vera is classified as a myeloproliferative disease. Symptoms include headaches and vertigo, and signs on physical examination include an abnormally enlarged spleen and/or liver. In some cases, affected individuals may have associated conditions including high blood pressure or formation of blood clots. Phlebotomy is the mainstay of treatment.
A hallmark of polycythemia is an elevated hematocrit, with Hct > 55% seen in 83% of cases.
B) Secondary Polycythemia
Secondary polycythemia is caused by either natural or artificial increases in the production of erythropoietin, hence an increased production of erythrocytes. In secondary polycythemia, there may be 6 to 8 million and occasionally 9 million erythrocytes per cubic millimeter of blood. Secondary polycythemia resolves when the underlying cause is treated.
Secondary polycythemia in which the production of erythropoietin increases appropriately is called physiologic polycythemia.
Conditions which may result in a physiologically appropriate polycythemia include:
- Altitude related
- Hypoxic disease-associated
- Iatrogenic
- Genetic - patients who have a special form of hemoglobin known as Hb Chesapeake, which has a greater inherent affinity for oxygen than normal adult hemoglobin. This reduces oxygen delivery to the kidneys, causing increased erythropoietin production and a resultant polycythemia. Hemoglobin Kempsey also produces a similar clinical picture. These conditions are relatively uncommon.
