The current urine test is ‘not fit for purpose’ and should be changed, scientists said in the British Medical Journal online.
An analysis found that different thresholds should be set according to ethnic group because of the prevenance of a certain genetic fault varies in each.
The genetic fault could allow an athlete to take testosterone to enhance their performance but still test negative for doping.
The fault is estimated to be present in one fifth of the African population, eight out of ten Asians, ten per cent of Caucasians and seven per cent of Hispanics.
Sport testing authorities set a ratio of testosterone to epitestosterone glucuronide concentration (T/E) at four, with anything above that triggering an investigation for possible doping.
The genetic fault affects how the body breaks down testosterone so an athlete with the fault could take the substance but still have a T/E ratio of less than four.
Research from the Laboratory for Doping Analyses, University Centre of Legal Medicine, in Switzerland, calculated that the threshold should be set at 5.6 for African athletes, 3.8 for Asians, 5.7 for Caucasians and 5.8 for Hispanics.
The study was carried out on 171 professional football players.
Research author Dr Christophe Saudan and colleagues said it would be better to track individual athletes’ own ratios over time and look for changes. Genetic profiling should also be used to determine cases where disparities remain.
He write: “These results demonstrate that a unique and non-specific threshold to evidence testosterone misuse is not fit for purpose.”
Prof Vivien James, emeritus professor of chemical pathology at Imperial College London said it would not be practical to enforce.
He said: “There are ethnic differences in people in the way they handle testosterone and this could provide a method for some people to get under the radar of the drug testing system. Introducing a passport would be a more secure way of monitoring T/E ratios over time so you could look for disturbances in the pattern.”
Prof Peter Sonksen, Emeritus Professor of Endocrinology St Thomas’ Hospital and King’s College London, said the ratios proposed by the research authors would probably not be acceptable in professional sport because it would mean one ‘clean’ athlete would wrongly test positive for doping for every 100 tests carried out.
He added: “It’s not all bad news, however; the increasingly popular ‘athlete’s passport’ and ‘I’m clean’ approach to doping control, where an athlete builds a profile of his/her own metabolism over time as the results of samples accumulate, will allow ‘athlete specific’ reference ranges to be established and these will clearly be lower in people with the gene mutation.
“With this approach it should make the testing more fair and less influenced by ethnicity.”
A spokesman for UK Sport, the national anti-droping organisation, said: “We have already been working on Steroid Profiling, through which we can pick up anomalies in an athlete’s profile which might not necessarily mean prohibited substances are showing up at levels sufficient for them to return elevated T/E, but they provide information which might suggest the need for further investigation or targeted testing."