Oligocene is a decrease in the number of formed elements (often mean erythrocytes) per volume of blood. Cause of oligocythemia can be: bleeding, insufficient production of blood cells (intoxication, diseases of blood-forming organs) and excessive destruction (hemolysis, hypersplenism, etc.).

Oligocene (oligocythaemia; from the Greek. oligos - small, poor, kytos - cell and haima, blood)- reducing the total quantity of formed elements in the peripheral blood. Depending on the total number of blood there are three forms of oligocythemia: normovolemicescoy, giperbolicheskoi and hypovolemic. Normovolemicescoy O. characterized by a decrease in the number of formed elements in normal amounts of blood and is observed in many diseases of the blood (hemolytic and chronic posthemorrhagic anemia). When giperbolicheskoi oligocythemia noted the low number of blood cells by increasing the mass of the blood, which is observed in diseases of the kidney with the presence of edema, diseases of cardiovascular system with circulatory insufficiency of II degree and in some periods various georegistration anemia. Hypovolaemic (olisemeka) O. occurs most often forms O. and is characterized by a low number of formed elements in the reduction of mass of blood.