context: Blood doping is an illicit method of improving athletic performance by artificially boosting the blood's ability to bring more oxygen to muscles. In many cases, blood doping increases the amount of hemoglobin in the bloodstream. Hemoglobin is an oxygen-carrying protein in the blood. So increasing hemoglobin allows higher amounts of oxygen to reach and fuel an athlete's muscles. This can improve stamina and performance, particularly in long-distance events, such as running and cycling. Blood doping is banned by the International Olympic Committee and other sports organizations. The three widely used types of blood doping are: blood transfusions injections of erythropoietin ( EPO) injections of synthetic oxygen carriers Here are some more details about each of these types of blood doping: Blood transfusions. In normal medical practice, patients may undergo blood transfusions to replace blood lost due to injury or surgery. Transfusions also are given to patients who suffer from low red blood cell counts caused by anemia, kidney failure, and other conditions or treatments. Illicit blood transfusions are used by athletes to boost performance. There are two types. Autologous transfusion. This involves a transfusion of the athlete's own blood, which is drawn and then stored for future use. Homologous transfusion. In this type of transfusion, athletes use the blood of someone else with the same blood type. EPO injections. EPO is a hormone produced by the kidney. It regulates the body's production of red blood cells. In medical practice, EPO injections are given to stimulate the production of red blood cells. For example, a synthetic EPO can be used to treat patients with anemia related to chronic or end-stage kidney disease. Athletes using EPO do so to encourage their bodies to produce higher than normal amounts of red blood cells to enhance performance. Synthetic oxygen carriers. These are chemicals that have the ability to carry oxygen. Two examples are: HBOCs (hemoglobin-based oxygen carriers) PFCs (perfluorocarbons) Synthetic oxygen carriers have a legitimate medical use as emergency therapy. It is used when a patient needs a blood transfusion but: human blood is not available there is a high risk of blood infection there isn't enough time to find the proper match of blood type Athletes use synthetic oxygen carriers to achieve the same performance-enhancing effects of other types of blood doping: increased oxygen in the blood that helps fuel muscles. There are tests to detect some types of blood doping, but not all. Here's a roundup of testing for different types of blood doping: Autologous transfusions. Currently, no test exists to directly detect autologous transfusions. Instead, indirect methods are used. One indirect method involves comparing an athlete's blood profile at testing time to blood samples collected at previous times. Significant differences between the two indicate possible blood doping. Known as the Athlete Passport, this method is endorsed by the World Anti- Doping Agency ( WADA). Homologous transfusions. Blood doping via homologous transfusion can be detected by testing. The tests were used at the 2004 Summer Olympic Games in Athens, Greece. EPO injections. Blood and urine tests can detect the presence of synthetic EPO. But EPO remains in the body for a very short time, while its effects last much longer. This means that the window for testing can be quite brief. Additional testing methods aimed at detecting new forms of EPO are currently being researched. Synthetic oxygen carriers. A test is available that can detect the presence of synthetic oxygen carriers. It was first used in 2004. By increasing the number of red blood cells, blood doping causes the blood to thicken. This thickening forces the heart to work harder than normal to pump blood throughout the body. As a result, blood doping raises the risk of: blood clot heart attack stroke An estimated 20 European cyclists are believed to have died as a result of blood doping over the past 25 years. Blood doping via transfusion carries additional risks. Tainted blood can spread infectious diseases such as: HIV hepatitis B hepatitis C Over time, repeated blood transfusions can cause a dangerous buildup of iron in the body. Improperly stored blood and improperly administered transfusions can cause acute lung injury and bacterial infection. Blood transfusions also have potential side effects of: allergic reactions fever rashes or hives The risks of EPO injections include: hyperkalemia (potentially dangerous elevation of plasma potassium levels in the body) high blood pressure mild flu-like symptoms Athletes who use synthetic oxygen carriers have an increased risk of: heart disease stroke heart attack blood clot