Transgender runner CeCe Telfer has been ruled out of the US Olympic trials after failing to meet World Athletics standards regarding testosterone levels, USA Track and Field said Thursday.

Telfer, who was due to compete in the opening heats of the women's 400m hurdles on Friday, was unable to provide evidence that she met testosterone thresholds laid out by World Athletics in 2019. 

The World Athletics standards on transgender athletes apply to all events.

They are separate to the rules that apply to women athletes with unusually high levels of testosterone, who are prohibited from competing in distances between 400m and a mile unless they undertake treatment to lower their testosterone levels.

USATF confirmed that Telfer had not demonstrated her eligibility to race at the trials in Eugene, Oregon, this week.

The federation said Telfer had been notified of the eligibility requirements prior to the trials but was not able to show compliance. 

"USATF strongly supports inclusivity and providing a clear path to participation in the sport for all, while also maintaining competitive fairness," the federation said in a statement. 

"If CeCe meets the conditions for transgender athlete participation in the future, we wholeheartedly back her participation in international events as a member of Team USATF."