A blood deficiency. Anaemia is, effectively, reduced levels of the red blood pigment haemoglobin. Since this occurs in red blood cells (Erythrocytes are red blood cells and contain the blood pigment haemoglobin. Red blood cells are responsible for transporting oxygen from the lungs into the cells of the tissues. They are predominantly produced in the bone marrow of larger bones....), a lack of red blood cells (erythrocytes) is often associated with a lack of blood pigment. The blood pigment transports oxygen in the blood, so a deficiency is associated with insufficient oxygen supply to the body. Anaemia can have many causes, including iron deficiency, increased loss of red blood cells (severe blood loss, tumours, chronic diseases), disorders in the synthesis of red blood cells (lack of Erythropoietin, abbreviated to EPO, is a growth factor that stimulates red blood cell production. EPO can be produced biotechnologically and administered for kidney failure or after chemotherapy.... in chronic kidney disease, bone-marrow tumours) and congenital disorders.