GENEVA -- Tyler Hamilton will keep his Olympic cycling gold medal because a backup drug test was inconclusive, the International Olympic Committee said Thursday.
Hamilton tested positive for signs of blood doping in the initial sample Aug. 19 after his time-trial victory in Athens. But analysis of the backup sample failed to confirm the original finding because of "lack of enough intact red blood cells," the IOC said in a statement from its Lausanne headquarters.
As a result, the IOC said it had dropped its investigation into the case and "would not be pursuing sanctions regarding this matter."
IOC medical commission chairman Arne Ljungqvist said the Athens lab made a mistake by deep-freezing Hamilton's blood sample rather than simply refrigerating it. As a result, the specimen deteriorated and the backup sample could not be analyzed, he said.
"It was a case of human error ... an unfortunate accident," Ljungvist said in a conference call.
Asked whether Hamilton had been lucky to slip through the net, he said, "It's up to everyone to draw his own conclusions on that."
Though Hamilton was cleared of any Olympic doping violation, a similar backup blood test came back positive from the Spanish Vuelta, his Swiss racing team Phonak said. That test was conducted Sept. 11.
The tests allegedly showed evidence of a blood transfusion from another person, Phonak has said. Blood transfusions can boost endurance by pumping oxygen-rich red blood cells to the muscles.
Usually an athlete is punished only when two samples from the same event test positive.
It was unclear whether the International Cycling Union would take action against Hamilton for the positive tests in Spain. If found guilty of blood doping, the 33-year-old American could face a two-year ban from the sport.
The IOC said it was informed Aug. 22 by the drug-testing laboratory in Athens that Hamilton's blood sample produced a "suspicious result." A group of experts studied the case and concluded Sept. 16 that the sample was positive.
The IOC set up a disciplinary panel to deal with the case, which could have led to Hamilton being disqualified and stripped of his medal. But the IOC said it was informed Wednesday that Hamilton's backup sample was "considered as nonconclusive." On Thursday, the panel decided to dismiss the case.
However, the IOC said, "The fact that the analysis of the B sample was not conclusive does not challenge the accuracy of the analysis of the A sample."
The IOC said the testing method used in Athens was authorized by the World Anti-Doping Agency after being validated by international scientists. WADA chief Dick Pound said he was surprised by the different test results.
"We're perfectly satisfied that the test properly implemented is entirely reliable," he told The Associated Press. "But how the test was applied or what was analyzed and all that sort of stuff, I don't know."
Hamilton said Tuesday he was innocent and denied receiving a transfusion. He repeated the denials Thursday.
Cycling's governing body had informed cyclists at the start of the season that it planned to start using a new blood-screening machine in the tests that detects blood transfusions, human growth hormone and synthetic hemoglobin. Until now, there has been no foolproof test for detecting blood transfusions.
Phonak plans to investigate the accuracy of the new tests.
"Since the new method is an effort based on probability and interpretation measurements, uncertainties will remain in this examination and procedure in any case," Phonak said.
"The team's goal is, and this is in the exact interest of Tyler Hamilton, that we have clarity in the end," it said. "The team management believes that it can form part of the campaign against blood doping and bring this matter up to a worldwide acceptable level."