Never failed a drug test?

http://amarillo.com/news/latest-news/2012-10-10/11-teammates-testified-case-against-armstrong
I was so hoping that Lance Armstrong would be able to clear himself of the long-held belief that he won all those Tour de France titles with the aid of chemicals.
Now the anti-doping agency that’s been probing the allegations against Armstrong says it has mounting evidence the bicyclist doped himself up to prepare for what arguably is the most arduous athletic endurance event on the planet.
Armstrong recently declared his intention to quit fighting the allegations, which many have described as an implied admission of guilt.
This is a heartbreaking turn. The agency’s contention that it has evidence that incriminates the Texan makes it even worse.
Here’s what has troubled me, though, from the beginning of this doping controversy. It’s been the nature of Armstrong’s so-called “denial.” His answer seems almost like a rote response. He keeps saying he’s “never failed a drug test.” I don’t ever recall him denying categorically ever taking performance-enhancing drugs. His response has been simply that he’s passed all the tests administered to him. And that begs the obvious question: Has the one-time cycling icon been gaming the system, enabling him to pass these tests with what amounts to a “false negative”?
If all this comes to pass and the governing body that is supposed to watch over this misbehavior determines that Armstrong cheated to win the Tour de France, removing Armstrong’s titles will create a gaping hole in the roll call of past champions.