]20 World Anti-Doping Code •20092.1.2 Sufficient proof of an anti-doping rule violationunder Article 2.1 is established by either of thefollowing: presence of a Prohibited Substanceor its Metabolite s or Marker s in the Athlete ’s ASample where the Athlete waives analysis ofthe B Sample and the B Sample is notanalyzed; or, where the Athlete ’s B Sample isanalyzed and the analysis of the Athlete ’s BSample confirms the presence of theProhibited Substance or its Metabolite s orMarker s found in the Athlete ’s A Sample .2.1.3 Excepting those substances for which aquantitative threshold is specifically identifiedin the Prohibited List , the presence of anyquantity of a Prohibited Substance or itsMetabolite s or Marker s in an Athlete ’s Sampleshall constitute an anti-doping rule violation.2.1.4 As an exception to the general rule of Article2.1, the Prohibited List or InternationalStandard s may establish special criteria forthe evaluation of Prohibited Substance s thatcan also be produced endogenously.