Was it dodgy meat or a blood transfusion? As the debate around three-time Tour de France winner, Alberto Contador's positive drug test heats up, Dr Ross Tucker weighs in on it.
Some have argued that transfusion theory is unlikely because the half-life of clenbuterol is so short (one day) that a cyclist would have to remove the blood within a day or two of having taken the drug in order for it to present in the sample at a later stage when that blood is re-infused.
The problem with this theory is that the concentration detected was so small that it's possible that the blood removal happened a few days after taking the drug, leaving only very small amounts in the blood, but that when it was re-infused, there was just enough to produce the positive test.
Remember, the lab that tested the sample may be one of the only labs in the world that could pick up this amount - so if a blood transfusion was done, it may have been thought to be safe because of the small 'dosage'.
Where this theory does have some legs is that the methods of blood doping are now so sophisticated - they have to be in order to fly under the radar of the biological passport system - that this would represent a very basic blunder.
I'm not suggesting people don't make those mistakes, but I'd be surprised at this particular one. Transfusion remains a real possibility - the best explanation so far, I'd hazard, but it's not that simple - I think there are still some issues around the pharmacokinetics of how that amount would appear in the urine.