My patient’s imunoassay test is negative but the mass spectrometry result is positive. How can this occur?
Immunoassays have cutoffs set at levels that can detect the presence of a drug AND its metabolites, whereas mass spectrometers have cutoffs which are set lower in order to detect EACH of that drug’s metabolites. For example, a patient is taking codeine. The immunoassay shows that they are positive for the class of drugs termed opiates. On the Mass Spec the patient sample tests positive for Codeine, morphine, and hydrocodone at lower levels than the immunoassay.
