Every assay vendor will disclose a list of drugs that can cross-react with their immunoassay. This information is essential for the proper interpretation of immunoassay results. In the immunoassay example on the right, morphine is defined as the standard (100%). Notice that some drugs, such as codeine, are detected more easily than morphine with this assay. Yet some drugs, like oxycodone, oxymorphone, and meperidine, cross-react less than15%. That is, these drugs will not be detected with sufficient sensitivity using this opiate screen. Thus, in this example, multiple immunoassay screens will be needed to detect the common opiates used in pain management.
Laboratory personnel need to educate clinicians on how to use the laboratory's drug screen. Laboratories may want to note in the patient results which drugs of the same class are NOT detected using their particular immunoassay. They should also supply an interpretation table so that clinicians can interpret results and so that they will become aware that one assay cannot detect all drugs of a given class.
