Red blood cells carry oxygen throughout the body, so it makes sense that if an athlete can increase his red blood cell count, he'll deliver more oxygen to his muscles and perform at a higher level. Blood doping -- removing and preserving a supply of blood so it can be returned, via transfusion, to the body right before competition -- is one way to do this, but it's messy and time-consuming. Taking erythropoietin, or EPO, increases red blood cell production without the need for transfusions. The kidneys make the hormone naturally, although people with severe kidney disease don't have enough. That's what the biotechnology firm Amgen was looking to address when it introduced synthetic EPO in 1985. By the 1990s though, cyclists and other endurance athletes had discovered that they could train longer and harder if they took the drug regularly.
Not surprisingly, taking EPO comes with significant risk. Yep, significant risk. Studies have shown that it increases the risk of events such as stroke, heart attack and pulmonary edema. One theory suggests that the drug thickens the blood to the point where it produces fatal clots. Such complications may have contributed to the deaths of at least 20 cyclists by 2000, increasing the urgency to develop a reliable test to detect EPO [source: Zorpette].
In 2007, anti-doping agencies introduced the concept of a "biological passport," a record of the substances found normally in an athlete's blood and urine, created by repeated sampling over time. By comparing the results of a blood test administered right before a competition to the passport, officials can determine if an athlete has been using EPO or other performance-enhancing drugs.