The World Anti-Doping Agency (Wada) says it is "very alarmed" after fresh allegations of suspected doping emerged in a leak of test data.
The Sunday Times and German broadcaster ARD/WDR have obtained access to the results of 12,000 blood tests from 5,000 athletes between 2001 and 2012.
According to the experts, the database reveals:
A third of medals (146, including 55 golds) in endurance events at the Olympics and World Championships between 2001 and 2012 were won by athletes who have recorded suspicious tests. It is claimed none of these athletes have been stripped of their medals.
More than 800 athletes - one in seven of those named in the files - have recorded blood tests described by one of the experts as "highly suggestive of doping or at the very least abnormal".
A top UK athlete is among seven Britons with suspicious blood scores.
British athletes - including Olympic champion heptathlete Jessica Ennis-Hill - have lost out in major events to competitors who were under suspicion.
Ten medals at London 2012 were won by athletes who have dubious test results.
In some finals, every athlete in the three medal positions had recorded a suspicious blood test.
Russia emerges as "the blood testing epicentre of the world" with more than 80% of the country's medals won by suspicious athletes, while Kenya had 18 medals won by suspicious athletes.
Stars such as Britain's Mo Farah and Jamaican sprinter Usain Bolt recorded no abnormal results.
Athletes are increasingly using blood transfusions and EPO micro-doses to boost the red cell count.
http://www.bbc.co.uk/sport/0/athletics/33749208