Athlete Steroidological Passport
This snapshot has been obtained from the Athlete Biological Passport software. It represents the longitudinal profile of the marker Testosterone over Epitestosterone ratio. Most male athletes present a T/EpiT ratio around 1.0, i.e. a similar concentration of testosterone and epitestosterone in urine. Some rare athletes with a particular genetic condition may present nevertheless higher or lower natural values of T/EpiT.
The blue lines represent the results of the tests on a single individual. This male athlete has been tested 6 times. The red lines present the personal limits on the expected values of the T/EpiT given the information available on the passport for a specificity of 99%. The initial upper limit that applies for a first test is 6.9. This limit guarantees a higher specificity than the value used today at 4.0. The limits become progressively individual in the course of evidence acquisition from multiple individual T/EpiT data. From a statistical perspective, this individualization corresponds to the nullification of the between-subject variance of the marker. If a new 7th test is carried out for this athlete, the individual limits that will apply are 0.5 and 1.5. A very narrow range is obtained because of the high stability of the T/EpiT ratio in a single individual. With a natural T/EpiT ratio at 1.0 and an upper individual limit at 1.5, there is no room for this athlete to monitor his T/EpiT profile with low doses of testosterone.
The colour bar shown below the graph represents at which percentile the whole sequence of 6 values – rather than one single value – is in the probability distribution of sequences expected from controlled, clean athletes when the testing protocols specific to the passport are followed.
The figure below shows the sensitivity – ability of the test to detect true positives in a population of doped athletes – and specificity – ability of the test to detect true negatives in a population of clean athletes – for (1) a limit fixed at 4.0, (2) the limits found with a longitudinal Bayesian approach with specificity fixed at 99%, (3) the limits found with a longitudinal Bayesian approach with specificity fixed at 99.9%. The same data obtained from the same longitudinal clinical trials involving volunteers doped with low (oral) doses of testosterone with the same marker are used, only the method of interpretation differs here. The Bayesian approach not only decreases the number of false positives by a huge factor, it also increases significantly the sensitivity to the abuse of small doses of testosterone. Additional information stored in an ASP such as UGT2B17 genotype and/or ethnicity and compliance with stricter protocols can still lead to a better efficacy of the T/EpiT ratio.