Polycythaemia - elevated red blood cell count
What is polycythaemia?
Having a high concentration of red blood cells in the blood is called polycythaemia. People with this condition have thicker blood, which makes it harder for blood to circulate around the body.
What are the symptoms of polycythaemia?
Mild cases of polycythaemia may not cause symptoms, but common symptoms include:
- Blurred vision
- Chest pain
- Muscle pain
- Ruddy complexion
- High blood pressure
- Tinnitus or ringing in the ears
If polycythaemia is related to kidney cancer, liver cancer, or other erythropoietin-secreting tumours, the symptoms of these conditions, such as weight loss, abdominal pain or fullness, or jaundice may be predominant.
Types of polycythaemia
Primary polycythaemia: In primary polycythaemia the increase in red blood cells is due to inherent problems in their production.
Secondary polycythaemia: Secondary polycythaemia generally occurs as a response to other factors or underlying conditions that promote red blood cell production.
Red cell production (erythropoiesis) takes place in the bone marrow through a complex sequence of tightly regulated steps. The main regulator of the red cell production is the hormone erythropoietin (EPO). This hormone is largely secreted by the kidneys, although, about 10% may be produced and secreted by the liver.
Erythropoietin secretion is up-regulated in response to low oxygen levels (hypoxia) in the blood. More oxygen can be carried to tissues when erythropoietin stimulates red blood cell production in the bone marrow to compensate for the hypoxia.
Neonatal ( newborn) polycythaemia can be seen in 1% to 5% of newborns. The most common causes may be related to transfusion of blood, transfer of placental blood to the infant after delivery, or chronic inadequate oxygenation of the foetus (intrauterine hypoxia) due to placental insufficiency.
What are the causes of primary polycythaemia?
Primary polycythaemia is due to acquired, or inherited, genetic mutations, causing abnormally high levels of red blood cell precursors. Primary familial and congenital polycythaemia and polycythaemia rubra vera are in this category.
Polycythaemia rubra vera
Polycythaemia rubra vera is a rare condition typically associated with abnormally high levels of red blood cells and often an elevated white blood cell count (leucocytosis) and platelet count (thrombocytosis). An enlarged spleen (splenomegaly) and low erythropoietin levels are other clinical features of polycythaemia rubra vera.
Primary familial and congenital polycythaemia (PFCP)
Primary familial and congenital polycythaemia (PFCP) is also thought to be caused by genetic mutations resulting in increased responsiveness to normal levels of erythropoietin. Most cases are caused by different mutations to the EPOR gene.
What are the common causes of secondary polycythaemia?
Secondary polycythaemia is usually due to increased erythropoietin (EPO) production either in response to chronic hypoxia (low blood oxygen level) or from an erythropoietin-secreting tumour.