- EQAS  samples for Threshold Substances   For Threshold Substances , the concentration in the EQAS  sample will be guided by, but not limited to, one of the following criteria:  o Greater  than (>) 50% of the Threshold  as established in the relevant Technical Document (s) or Laboratory Guidelines ; o At less than (<) 50% of the Threshold  for those exogenous Threshold Substances  specified in the TD DL whose presence shall be reported if detected in the presence of diuretics or masking agents.