The term polycythemia means there is an elevation of hemoglobin above the normal level. Blood contain cellular components and fliud compartment .One of the cellular component is RBC (red cell corpuscles )and the fluid compartment is called plasma. Hemoglobin elevation can be absolute or relative. The term relative means elevation in hemoglobin is secondary to decrease in plasma volume that is fluid part of blood. RBC cell mass is measured as PCV (packed cell volume )or hematocrit. It is a disease of middle aged people or elderly
Criteria for diagnosis of polycythemia are given below
Hemoglobin level - more than 17 g/dLfor men.
Hemoglobin level - more than 15 g/dL for women.
Hematocrit levels > 50% in men.
Hematocrit levels > 45% in women may be abnormal.
Hematocrits > 60% in men and >55% in women is definitely associated with Elevated RBC mass.
Elevated PCV in a patient with true polycythaemia due to congenital cyanotic heart disease (left) compared to a blood sample taken from a person with a normal PCV (right ). Dark part represent the RBC mass, yellow part the plasma. In the first one there is a rise in RBC mass representing polycythemia.It is very important to identify whether the polycythemia is true or apparent. True polycythemia can be primary or secondary.
Apparent or spurious polycythaemia
In apparent or relative polycythaemia RBC mass is not elevated and the increased packed cell volume is secondary to a fall in the plasma volume. It may be associated with dehydration smoking, excess alcohol intake, obesity, diuretics, and hypertension.
True polycythemia
Polycythaemia vera is the term given to Primary polucythemia. Exact cause not known, genetic factors play a significant role.
Secondary polycythaemia
Here the rise in hemoglobin is secondary to definite cause. There are a variety of secondary causes of polycythemia most common is decreased oxygen content of blood and disease of kidney, cigarette smoking. Other causes are given in the table below.
Relative polycythaemias
Hemoconcentration secondary to dehydration, diuretics, ethanol abuse, androgens or tobacco abuse
Causes of Absolute polycythaemias are the following
1.Hypoxia is seen in
Carbon monoxide intoxication
High oxygen-affinity hemoglobin
High altitude
Pulmonary disease
Right to left cardiac or vascular shunts
Sleep apnea syndrome
2.Renal Disease
Renal artery stenosis
Focal sclerosing or membranous glomerulonephritis
Postrenal transplantation
Renal cysts
3.Tumors
Hypernephroma
Hepatoma
Cerebellar hemangioblastoma
Uterine myoma
Adrenal tumors
Meningioma
Pheochromocytoma
4.Drugs
Androgens
Recombinant erythropoietin
Detection of polycythemia is important irrespective of the cause because when there is a rise in hemoglobin or RBC mass it increase the the whole blood viscosity. As a result of rise in viscosity there can be reduction of blood supply to the organ and reduced oxygen supply which in turn lead to a variety of clinical symptoms.
