The World Anti-Doping Agency (WADA) has voiced concerns regarding the protection of clean sport in the United States, calling for "root and branch" reforms of the anti-doping system within the country, especially in college sports.

According to a WADA letter that was sent to U.S. Anti-Doping Agency (USADA) board chair Tobie Smith last Friday, 90 percent of all athletes in the United States compete outside the protection of the World Anti-Doping Code.

WADA said it received a letter in July on behalf of 32 national and regional anti-doping organizations from Europe, Asia and Africa who are concerned the U.S. is sending athletes to major events like the Olympics and world championships without being sufficiently tested in advance.

"It is surely time to address these issues that directly concern USADA and U.S. athletes," WADA said.