A backup B-sample confirms Frank Schleck tested positive for a banned diuretic at the 2012 Tour de France, but the Luxembourg rider insisted Friday he is not guilty of doping.

The RadioShack Nissan Trek leader was pulled from the Tour on Tuesday after the International Cycling Union said he had tested positive for the banned diuretic Xipamide on July 14. He was in 12th place overall, 9 minutes, 45 seconds behind leader Bradley Wiggins.

The diuretic is classified as a specified substance and does not require a provisional suspension. The World Anti-Doping Agency defines "specified substances" like Xipamide as those that are "more susceptible to a credible, nondoping explanation."

Bans for such substances are often shorter, and athletes have a better chance of proving they did not intend to consume it or enhance their performance.

Athletes who dope often take diuretics like Xipamide to mask other banned performance enhancers, or as a supplement for weight loss.