It is illegal for athletes to take steroids or any other type of drugs, so they are relying on blood doping. Right before an event, an athlete will blood dope. By doing that they take a substance to enhance the red blood blood cell count. As the erythrocytes go up the oxygen is easily transported to the muscle making the performance of the athlete better. The main type of substances used for blood doping are synthetic oxygen carriers, blood transfusions, and erythropoietin (EPO). Purified proteins or chemicals having the ability to carry oxygen are known as synthetic oxygen carriers. Some examples of them are haemoglobin based oxygen carriers (HBOCs) or perfluorocarbons (PFCs). Doing this brings the risk of cardiovascular disease. Synthetic oxygen carriers are mainly used in emergency when human blood is not available, but the risk of crossing different types of blood is high. Fortunately, there is a test that was created in 2004 to indicate if the form of blood doping is being used. Blood transfusions are a less common form of blood doping. The two types of blood transfusions used are autologous and homologous. Autologous is when an athlete uses their own blood. They refrigerate or freeze the blood and right before an event they do a transfusion. This process hold many risk factors. The blood has to be stored correctly in order to stay viable and the procedure must be done correctly. Homologous blood transfusions involve another humans blood with the same blood type. This brings the risk of virus which passed through the transfusion. Blood transfusions as a form of blood doping dates back decades but there is only a test to detect if the homologous form is being used. Erythropoietin (EPO) is a natural human hormone produced by the kidney and stimulates red blood cells from the bone marrow. The red blood cells go directly to the muscle and may cause the body’s capacity to buffer lactic acid to increase. If a human has anemia related to kidney disease EPO can be used therapeutically in the right matter. But for an athlete, EPO in the form of blood doping is not the right matter. The use of EPO can lead to heart disease, stroke, and cerebral or pulmonary embolism due to the thickening of the blood. In some cases, autoimmune diseases have been brought for EPO. a test from 200o was able to detect the use of EPO through blood and urine. Then, in 2003, a test just using urine to detect the use was developed.