Validate the interest of testing the hair of an athlete challenging his/her anti-doping violation in a situation of contamination.

A low or a very low urine concentration can be interpreted in two different ways: (1) it can be the tail end of a drug used to enhance performance; or (2) it is the direct consequence of a contamination. By contamination, one can include laced supplements, contaminated meat by growth promoters, poor quality pharmaceuticals and finally drug transfer during intimate moments.

When using hair tests in the field of anti-doping, the question of importance is to know whether the analytical procedure is sensitive enough to identify traces of drug(s) in hair after exposure, even in single drug exposure. It has been accepted that a negative hair result cannot exclude the administration of a particular drug, or one of its precursors and that the negative findings should not overrule any positive urine result. Nevertheless, the negative hair findings can, on occasion, cast doubt on the positive urine analysis, resulting in substantial legal debate and various consequences for the subject and the final response to the sport authorities, lawyers, or judges.

Testing for doping agents in hair allows discriminating cheating from contamination based on the measured concentration or even the absence of the target drug. Hair is receiving more and more attention by scientists and lawyers due to is long detection window, particularly when compared to blood and urine, its less embarrassing conditions of collection and its storage at ambient temperature. By providing information on exposure to drugs over time, hair analysis may be useful in verifying self-reported histories of drug use in any situation in which a history of past rather than recent drug use is desired. Hair analysis can also provide a retrospective calendar of an individual's drug use. For this, multi sectional analysis is required and involves taking a length of hair and cutting it into sections to measure drug use during shorter periods of time.

Applications and limitations of hair tests in doping control have been extensively reviewed in several papers [1Kintz et al. Drug Test Anal, 2020.

Cliquez ici pour aller à la section Références] during the last years. In particular, it must be emphasized that a single exposure to some drugs, such as anabolic steroids, SARMs or diuretics is not detectable in hair. The authors can accept that some parameters about the detection of these agents in hair have not been addressed: dose necessary to give a positive result, repeatability, robustness, contamination, carry-over, interferences, variable incorporation into hair, external factors that may have an impact, etc. The minimum dose that had to be ingested by a subject in order to get a “positive” detection in one of the hair sections tested, one or two months after the collection of a urine sample, is unknown. However, for many other drugs, such as chlortalidone, trimetazidine, letrozole, a single exposure is detectable in hair. In case of challenging the AAF, an athlete (who has the burden of proof in doping control) is in his right to produce evidence for his/her defence. This has prompted athletes to get closer to the forensic side to produce alternative admissible elements to confirm their claims of unintentional doping. For the first time in 2009, the Court of Arbitration for Sports (CAS) has accepted hair test results in the Richard Gasquet case. In case of supplement or meat contamination, hair testing for the prohibited substance identified in urine during the control can also be useful. Numerous authentic cases, including several submitted towards CAS will be presented during this review.

In many cases, the WADA dogma goes against a scientific proof based on hair tests, and from a forensic perspective, this appears difficult to understand.

Because hair testing for drugs increases the window of detection and permits the differentiation of long-term use from a single exposure when performing segmental analyses, this matrix should be considered as a suitable complement, and not an alternative, to standard investigations.