Blood Doping: What It Is and Why Lance Didn't Get Caught

Updated: 01/18/2013 5:40 PM KSTP.com By: Ellen Galles

Blood doping is done through transfusions or through EPO injections. 

Athletes who do it try to increase their number of red blood cells, and ultimately their oxygen-carrying capacity so they can last longer and go faster.

Blood doping can be hard to detect because there aren't the physical symptoms that you see with other performance-enhancing drugs like steroids (common side effects are acne and aggressive behavior).

Since 2009 high-profile races the The Tour De France have tested the blood levels in athletes.