A condition of the blood in which there are quantitative and qualitative changes in the red cells (erythrocytes) and hemoglobin in the circulating blood and bone marrow: there may be also a reduction in the total amount of blood (dighoaemia). Defective red-cell formation due to deficency conditions produces macrocytic megaloblastic or microcytic normoblastic anaemias according to the deficiency; inhibition or aplasia of the haemopoietic tissues causes aplastic and hypoplastic anemias excessive red-cell destruction occurs in the haemolytic anaemias, while acute or chronic blood loss is followed by hypochromic anaemias.