Red blood cell; erythrocytes make up the majority of cellular blood components. They are formed in the bone marrow, contain haemoglobin (the red pigment in blood ) and have a life expectancy of about 120 days in healthy people. The haemoglobin content of the blood is an important measurement that provides information on e.g. whether a patient is anaemic. The function of haemoglobin (and therefore the erythrocytes) is to transport oxygen, which is taken up in the lungs, and carbon dioxide, which is released by the lungs.