such as: (a) substances used for patient treatment (e.g. therapeutic drugs, anticoagulants, etc.); (b) substances ingested by the patient (e.g. over the counter medications, alcohol, vitamins, foods, etc.); (c) substances added during sample preparation (e.g. preservatives, stabilizers); (d) substances encountered in specific specimens types (e.g. hemoglobin, lipids, bilirubin, proteins); (e) analytes of similar structure (e.g. precursors, metabolites) or medical conditions unrelated to the test condition including specimens negative for the assay but positive for a condition that may mimic the test condition (e.g. for a hepatitis A assay: test specimens negative for hepatitis A virus, but positive for hepatitis B virus).