hrotha said:
The idea is that blood can only be stored for so long before it becomes unusable. You can store it for months by centrifuging it, but then it wouldn't retain any traces of clen.
This is a good point. For those who don't know, long-term (i.e., more than a month or so) storage of blood requires separation of red cells from plasma, which are then stored separately frozen. It has been speculated that the elite riders, with access to the best resources, may use this method, because the alternative is to withdraw blood periodically during the racing season. Freezing blood in principle would allow a rider to withdraw blood one or more times during the offseason and save it for targeted transfusions during the season. As far as I know, though, there are no reliable reports confirming that any rider actually does this; someone may correct me on this.
Most of a drug like CB would be in the plasma. A portion of it would probably bind to red cells, but likely a fairly small fraction of the original amount in the bloodstream at the time of withdrawal. However, riders may use all or a portion of the plasma when they transfuse. All they need at a minimum is the red cells, which can be transfused with saline or some other artificial medium, but they might choose to use at least some of the plasma, as well. According to a source I consider reliable, when riders store withdrawn blood short-term for transfusion, more than half the plasma is removed. That is, if two units of blood were withdrawn, the red cells would be removed by centrifugation, then reconstituted with one unit or less of plasma for re-infusion. To re-emphasize, this is my understanding of what riders do when they withdraw blood for short-term storage, so my guess is they probably would do this for long-term storage as well.
So even if Bert did all his withdrawals in the offseason, many months before his hypothetical transfusion during the Tour, the blood might contain some CB. This is a point I had not thought of when I originally posted, hrotha's post reminded me of it. In fact, when the blood was withdrawn might not make much difference at all, except that upon long-term storage, CB may degrade somewhat. When the news of Bert's positive first broke, there was a some discussion on this forum about the long-term stability of CB, but I think the upshot was that no one really knows. From my experience as a lab scientist working with other substances, I would guess that CB stored in a frozen medium would probably be pretty stable. In fact, it would probably be more stable for a year frozen than a month refrigerated.
Anyway, the bottom line is that if Bert was taking CB when he withdrew blood for later transfusion, it probably would not much matter when that blood was withdrawn. Regardless of whether it was in the offseason, and stored frozen, or withdrawn as recently as after the DL in June, the plasma containing most of the CB would probably initially be separated from the red cells. Then upon re-infusion, the red cells would probably be reconstituted with some but not all of that CB containing plasma. (If a rider were really clever, he might realize this, and not use any of the plasma to reconstitute).
A little more on the hair test. The value of this test is its ability to determine if a drug was being taken during some period prior to when the test is actually conducted. If the detection sensitivity of the drug is good enough, it does not require that large amounts of the drug were taken over a long period of time. In principle even a one time, inadvertent consumption of CB, as from contaminated meat, might result in detection of CB in the hair. The idea is that from the amount present in hair it can be estimated how much CB was originally ingested, and in this manner distinguish from contamination and an intentional program of CB use.
So it's conceivable that a positive hair test, if the amount detected was very low, would not establish that Bert had been taking CB as part of a doping program. In fact, keep in mind that while the probability of eating CB-contaminated meat on any particular day, such as the rest day of the TDF, is remote, the odds go up somewhat for ingestion over a window of several months. Ingestion of CB at any time during this period might result in a positive hair test.
Now that CB can be detected at very low levels, it would be interesting to test the population at large to see if a significant number of people have positive hair tests. Just as levels of DEHP are found in virtually everyone, the same might be the case for CB.