The process – from obtaining the sample through to delivering what may be career-ending results back to athlete and coach – is highly sensitive and demands high levels of speed, skill and security.
Any of the more than 10,000 athletes can be required to test anytime, anywhere – trackside, poolside, in the athletes village or in private houses and whether they are already in Britain or still at training camps outside of the country.
The testing experience – which has the potential to bring shame and humiliation down on anyone caught cheating – starts when an Olympic anti-doping official approaches an athlete and tells them they’ve been selected.
It’s a conversation that will take place with thousands of athletes across all sports and nationalities and will include all medal winners, organizers say.
Many top athletes will face repeat tests before the Games end on August 12.
If they refuse to give a sample, athletes can be banned from coming to London to compete or they can be sent home, as Hungarian discus thrower Zoltan Kovago found out last week.
Those who agree to be tested are accompanied by a chaperone at all times until they get to a doping control station where samples are taken.
The athlete provides a sample – of either urine or blood -which is then split into two lots, A and B, so that one can be used for back-up testing if results on the A sample are queried.
The athletes themselves are required to seal the bottles and fill in the paperwork – a protocol designed to minimize the risk of contamination.
The sample bottles have tamper-proof seals that can only be opened using specialist equipment in the lab.