The primary function of red blood cells is to transport oxygen to the cells. Red blood cells do not contain a nucleus or other cell organelles. Therefore, red blood cells consist only of the cell membrane, enzymes and hemoglobin. Hemoglobin is an iron-containing protein that is specialized in binding oxygen. Hemoglobin gives the blood its red color. It is also capable of binding carbon dioxide, but most of the carbon dioxide released during cell respiration is transported in the blood itself.

Thanks to the biconcave shape of red blood cells, their combined oxygen absorption surface area is approximately 3,000 square meters, or the size of 15 large detached houses. When a red blood cell dies, its hemoglobin is transferred into new red blood cells or stored in the liver.

Anemia is a condition caused by either a decrease in production of red blood cells or hemoglobin. Its symptoms include tiredness and loss of appetite. Anemia can be caused by a deficiency of important nutrients or vitamins, such as iron, zinc or vitamins A and C.

Smoking increases the carbon monoxide (CO) content of your blood. CO can become attached to hemoglobin, which prevents the blood from carrying oxygen. Almost ten percent of the red blood cells of a regular smoker actually carry carbon monoxide instead of oxygen. This causes the smoker to be in a weaker physical condition than a non-smoker.

Blood Count	abbreviation	Reference value (that is, readings between values are considered normal)
Hemoglobin	B-Hb	men 130–165 g/l; women 115–150 g/l
Hematocrit	B-Ht	men 0,40–0,54; women 0,36–0,47
Red blood cell count: Erythrocytes	RBC	men 4,2–5,6 * 1012/l; women 3,8–5,1 * 1012/l
Leukocytes	Leu	3–8 * 109/l
Thrombocytes	B-Trom	150–350 * 109/l