For thousands of world-class athletes, a passport is something they can't forget to pack before heading off to London for the summer Olympic games. But for a few athletes, a different kind of passport is keeping them out of competition entirely.
A new anti-doping program known as the athlete biological passport (ABP), which looks for indirect evidence that an athlete has cheated, is being implemented by several international sports authorities. Already the testing scheme, developed by the World Anti-Doping Agency (WADA), has ensnared world-class athletes—and survived a challenge to its validity.
The London Olympics mark the first summer games in which the ABP will be in use alongside traditional drug screenings. And for competitors in sports that have taken up the program, such as cycling and track and field, dreams of Olympic glory will depend on their test results—past and present.
Rather than screening an athlete's blood or urine samples for traces of banned substances right before or after a competition, testers using the ABP scheme compare samples with an athlete's baseline profile, as determined by multiple tests over time. In the absence of a legitimate physiological explanation, such as an illness or a natural response to changing altitude, variations in an athlete's biological samples can reveal wrongdoing even if the specific doping agent or process remains undetected. For instance, a sudden change in the number of reticulocytes, or immature blood cells, might provide indirect evidence that an athlete has used erythropoietin (EPO), a hormone that stimulates the generation of red blood cells and boosts the oxygen-carrying capacity of the blood. Similar tests can assess levels of the respiratory pigment hemoglobin, which can also reveal instances of blood manipulation to enhance oxygen transport.
"In this way, the athlete becomes his own reference point," says WADA medical director Alan Vernec. "Otherwise you're forever chasing after new types of substances or agents that are being developed."
So far the biological passport has been applied primarily to detect instances of blood doping, but the same strategy could be used on urine samples to identify users of anabolic steroids. Nevertheless, the ABP is unlikely to supplant conventional testing schemes that detect prohibited molecules, such as steroids or human growth hormone, in blood and urine. Anti-doping experts view the passport approach as a complement to such tests, which continue to catch athletes breaking the rules.
Indeed, conventional testing still plays a significant role in cycling, the first major sport to sign on to WADA's passport approach. In the highest-profile recent case, Spanish cyclist Alberto Contador was issued a two-year suspension and stripped of his 2010 Tour de France win after a sample that year tested positive for clenbuterol, which WADA classifies as an anabolic agent.
The International Cycling Union (UCI), suffering from a severe credibility problem, adopted the ABP in 2008, collecting about 10 blood samples each from more than 800 riders over the course of the year. But implementation of the ABP has not been without twists and turns. Cyclist Franco Pellizotti, who raced for Italy in the 2008 Olympics, was suspended in 2010 for irregularities in his blood profile that indicated "enhancement of oxygen transfer." But the rider was soon exonerated by the Italian Olympic committee, which held that the evidence against Pellizotti was insufficient to prove his guilt.
The cycling union appealed to the Court of Arbitration for Sport (CAS) in Switzerland, which last year overturned the Italian committee's decision and reinstated Pellizotti's two-year ban from cycling. The court also upheld a two-year ban for Italian rider Pietro Caucchioli; the cyclist's variations in hemoglobin concentration over a span of several months, the court ruled, "could not be considered as physiological" and hence demonstrated doping to enhance the blood's oxygen-carrying capacity.