Former Phonak rider Tyler Hamilton has filed an appeal to world sport's top tribunal to overturn a two-year ban for blood doping, the International Court of Arbitration for Sport (CAS) announced on Wednesday. Hamilton, who won an Olympic gold medal in Athens just weeks earlier, tested positive for homologous blood transfusions – the injection of red blood cells from another person - during the Vuelta a España last September. Following a lengthy hearing in March, the U.S. anti-doping agency handed down a two-year suspension on April 18. Hamilton’s suspension expires in April of 2007, but new UCI ethics rules also add an additional two-year suspension from cycling’s top-tier ProTour teams. If upheld, the combination would essentially spell the end of the 33-year-old American’s career. "Hamilton requests CAS to annul the ... decision and to exonerate him from any penalty, considering that he did not commit any doping offence," the Swiss-based CAS noted in statement released on Wednesday.

The court is the final avenue of appeal in international sport. A ruling by a CAS panel of independent legal experts is normally issued within four months of an appeal being lodged. Hamilton had also submitted a blood sample after winning the individual time trial gold at the Athens Olympics. The first sample was ultimately deemed positive, but the finding could not be confirmed after the "B" sample for that test was destroyed when it was frozen.

The International Olympic Committee had already ruled that it could not strip Hamilton of his medal without a viable B sample as a back-up test. The Russian and Australian Olympic committees have filed an appeal to the CAS as well, arguing that Hamilton's positive in Spain lends credibility to the original positive in Athens. Hamilton's is the first case based on a test designed to detect the presence of someone else's red blood cells. A blood transfusion can increase endurance by providing extra oxygen-carrying red blood cells.

Such homologous blood doping is one of several means of enhancing endurance by increasing the amount of oxygen-carrying red blood cells in an athlete’s system. Autologous blood doping - the practice of withdrawing and reinjecting one's own blood - is not yet detectable. Both practices are prohibited under UCI rules and the World Anti-Doping Code.

Hamilton's former teammate, Vuelta runner-up Santiago Perez, is the only other athlete who has ever tested positive for homologous blood doping since the test was first used in the summer of 2004. Perez, too, is appealing his two-year suspension to CAS.

Hamilton has argued that the test used to determine blood doping had yet to be proven in an anti-doping context, and was unreliable. Much of Hamilton’s appeal is based on a rigorous dissent lodged by one of the three panelists hearing the case for USADA.The full text of the U.S. panel's decision is available at www.USAntidoping.org.

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