• Tour starts with time trial in Utrecht
• Boom rides for defending Tour champion Nibali's Astana team

UTRECHT: Dutchman Lars Boom will start Saturday's first stage of the Tour de France despite showing low levels of cortisol in a test on the eve of the race, his Astana team manager said.

Low levels of the hormone can be explained by the use of corticoids, anti-inflammatory drugs that are allowed out of competition but forbidden while racing unless a rider is granted a Therapeutic Use Exemption (TUE).

"Boom will take the start," Alexander Vinokourov told reporters.

Astana, the team of defending Tour champion Vincenzo Nibali, are members of the MPCC (Movement for Credible Cycling) that applies stricter rules than the International Cycling Union (UCI) and the World Anti-Doping Agency (WADA).

Under MPCC rules, Boom should be rested for eight days, meaning he should not start Saturday's 13.8-km time trial. UCI rules, however, do not forbid Boom from racing.

Astana's bid to replace Boom with Italian Alessandro Vanotti was denied by the UCI, who stated on Friday that the request had been made too late.

"Teams can't change their starting list after the sports directors' meeting has taken place," the governing body said in a statement.

"The UCI is committed to applying its regulations consistently and will therefore not authorise any team to change its starting list now."

His team said that Boom was healthy enough to start the Tour.

"Astana... received confirmation from the UCI that as a low cortisol result is no risk to the health of the rider, therefore there are no valid grounds for a late substitution," the Kazakh-funded team explained in a statement.

"Team medical staff have advised that Boom's low cortisol result is the consequence of a long-standing and well-known application of anti-asthma therapy by the athlete and is not a violation of UCI rules and regulations.

"Team medical staff have advised that there is no danger to the rider's health or safety to start the 2015 Tour de France."

Astana are no strangers to controversy, having come close to losing their World Tour licence this year following positive tests from Kazakh riders in the team.

Vinokourov, the 2012 Olympic road race champion, was himself kicked out of the 2007 Tour after twice testing positive for blood doping.