Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (636 page)

   The presence of opioid process impurities may explain apparent inconsistent results.

   Interpretation

   Drug not detected due to

   Drug not taken/administered

   Drug taken incorrectly (decreased dose or frequency)

   Variable drug delivery—drug not absorbed

   Accelerated metabolism, elimination

   Drug–drug interaction

   Specimen collected outside detection window

   Specimen dilute, substituted, adulterated

   Test not designed to detect drug

   Clinic or laboratory error

   Drug detected due to

   Drug was taken/administered.