LONDON (AP) -- NASCAR indefinitely suspended driver A.J. Allmendinger on Tuesday after confirming he violated its substance-abuse policy, putting his career and future with Penske Racing in jeopardy.
The suspension came after a test of his backup urine sample confirmed the original positive result.
Allmendinger originally was suspended July 7 after failing a random drug test taken in late June. His backup "B" urine sample was tested Tuesday by Aegis Analytical Laboratories in Nashville, Tenn.
NASCAR officials announced the result and subsequent suspension Tuesday night.
"While not a pleasant experience by any stretch of the imagination, we feel like we have one of the best drug testing programs in sports," NASCAR spokesman David Higdon said.
Allmendinger on Twitter thanked fans for their support.
"I'm sorry we even have to have this going on. But I promise I will do whatever it takes to get to the bottom of this and get back out there no matter what," he tweeted.
Officials did not announce what substance Allmendinger tested positive for. Allmendinger previously said he tested positive for a stimulant, but did not give specifics. He has denied knowingly taking a banned substance.
"This was not the news we wanted to hear and we will work to get to the source of what may have caused this," said Tara Ragan, Allmendinger's business manager, in a statement.
"To that end, we have secured the services of an independent lab to conduct thorough testing on every product within AJ's home and motor coach to find what might collaborate with his test, which created results that were within nanograms of accepted standards. We are working closely with NASCAR and Penske Racing to identify the next action steps in this process."
NASCAR officials did not say how far Allmendinger's positive test went beyond a predetermined range of acceptable levels - and as is the case in other sports drug testing programs, officials wouldn't consider it a valid defense if a competitor just barely exceeded acceptable levels of a banned substance.
"We choose not to disclose the level," Higdon said. "To us, a violation is a violation, and that's what happened here."
Given the indefinite nature of his suspension, Allmendinger's only avenue to return to NASCAR is to complete a "road to recovery" program. He will be issued a letter outlining a process for reinstatement, and must agree to the letter to participate in the program.
In a statement, Allmendinger's Penske Racing team acknowledged it had been notified of the test results.
"Penske Racing is very disappointed with the result of the B sample test and will evaluate its course of action as it pertains to AJ over the coming week," the team said.
The team said Sam Hornish Jr. will drive the No. 22 car this weekend at Indianapolis and next weekend at Pocono. Hornish has filled in for Allmendinger in the past two Sprint Cup Series races.
Allmendinger's primary sponsors, Shell and Pennzoil, called NASCAR's process and procedures "appropriate" in a statement.
"We share Penske Racing's disappointment with the result of AJ's B sample test and will work closely with them to determine plans moving forward," the sponsors said. "We hope for the best for AJ during this difficult time."
NASCAR's recovery program includes evaluation by a substance abuse professional to create a "road map" leading to a return to competition. The plan can include anything from counseling to in-house treatment and rehabilitation.
Additional testing is also required at the program administrator's discretion. Once the suspended competitor successfully completes the plan, the program administrator will send a letter to NASCAR recommending reinstatement.
Speaking to The Associated Press earlier Tuesday, before Allmendinger's B sample results were announced, NASCAR CEO Brian France he is confident in the series' drug testing program that once again came under scrutiny after Allmendinger's original failed test.
"We believe it's a strong testing system that works," France told The Associated Press in London, where the NASCAR executive will speak Wednesday at the Beyond Sports Summit. "We've got the best guy (David Black, Aegis' CEO) running the program, and it's a solid system that we believe does the job intended."
Because Allmendinger has said he tested positive for a stimulant, there has been speculation that it came from a supplement or energy drink consumed by the first-year Penske Racing driver. Allmendinger works out regularly and is known to be health conscious.
He is the second Sprint Cup Series driver suspended under the tightened policy implemented in 2009. Jeremy Mayfield was the first driver, and he unsuccessfully sued to have the results overturned.
NASCAR does not reveal the substance found in a positive test, but court documents showed it was methamphetamine that Mayfield had in his system.
France indicated Tuesday that NASCAR is unlikely to reconsider its policy of not revealing the substance.
Ragan thanked fans for supporting Allmendinger.
"We continue to be extremely grateful by the breadth and scope of support for AJ from his fans and partners," Ragan said. "We would like to again thank NASCAR, Penske Racing and all our sponsor partners for the open communication, and for helping us at every step in this process. We expect to have further updates in the upcoming days."