In an interview with Reuters during a anti-doping conference organized by the London law firm Hammonds LLP, Tygart said the out-of-competition positive test returned by British rugby league player Terry Newton was a significant advance.

"It reassures clean athletes that those like UK Anti-Doping and its equivalents around the world are doing everything possible to protect their right to compete on a level playing field," he said.

"It sort of confirms what we've said all along that the test is valid, scientifically sound, it's taken a lot of time and money to develop it but when's it's implemented it can be effective.

"So now I think there's a real call for sports around the world to start using it and you've got to do out-of-competition blood testing in order to catch someone who wants to use human growth hormone. That's an area that needs to grow." A test for HGH, an anabolic hormone which is also produced naturally in the body, was introduced at the 2004 Athens Olympics. Synthetic HGH, which was banned by the International Olympic Committee in 1989, is difficult to detect because it leaves the body quickly.

Tygart said the rugby league positive was conclusive proof that the test worked.

"It's a significant deterrent for athletes using human growth hormone but it's also going to detect those who use it.

"Hopefully this will give evidence that it's worth the time and the cost that collecting blood out of competition carries.

"It highlights the importance of collecting blood and collecting blood out of competition without advance notice so that athletes who are going to use it run a significant chance of being caught.