The solicitor for Ireland's triple Olympic champion has revealed the B test on the urine sample she gave had confirmed the findings of the A sample, which contained a potentially lethal dose of alcohol.
Her case is now expected to come before the doping panel of swimming's international governing body, Fina, next month, but even if she is found guilty it is not likely to be the end of the matter.
The 28-year-old, who as Michelle Smith won three gold medals at the Atlanta Olympics, has said she would then appeal to the Court of Arbitration for Sport in Switzerland, while a further move into the civil courts cannot be ruled out.
De Bruin's defence is likely to rest on her call for the governing body to prove that she was the one who manipulated the sample.
Her solicitor, Peter Lennon, who watched the analysis of the twin samples in the International Olympic Committee-accredited laboratory in Barcelona that carried out the original test, said: "It appears clear at this time that our client can only be charged with physical manipulation and not the use of any banned substance.... We do not expect there to be any change between the adulterisation results of the A and B sample."
The Dublin-born swimmer added that she was "more determined than ever" to fight any charges that may be formally brought against her.
Fina said yesterday they had not received the result of the back-up test, but a spokesman confirmed De Bruin could face a life ban for tampering with a test. There could be no retrospective punishment over her Olympic gold medals, however.
A Fina spokesman said: "The swimmer's solicitor can say what he wants, but we have not yet had the result from the laboratory, and until we do, we cannot comment.
"When we have the result, we will tell the swimmer first. We will then announce whether the matter will go before the doping panel. The penalty will be at the discretion of the panel, but for manipulation of a test it can be from zero to life."
De Bruin underwent an out-of-competition test on January 10 at Kilkenny in Ireland, when Fina said the A sample showed "unequivocal signs of adulteration" and "physical manipulation".
Prince Alexandre de Merode, chairman of the IOC's medical commission, said the sample included a potentially lethal concentration of alcohol, and that alcohol could be used to mask the presence of banned drugs. De Bruin has denied tampering with her test and said any manipulation must have taken place after it was out of her sight.
In the past De Bruin has said: "My success is down to one thing - hard work." Now she must labour to prove her innocence.Reuse content