The Good, the Bad, and the Ugly

The urine drug screen commonly utilized in the emergency department is an immunoassay that uses antibodies to detect specific drugs or their metabolites. This allows for rapid screening for drugs of abuse, but it has many limitations.   Gas chromatography-mass spectrometry (GC-MS) is the confirmatory test, but it is more costly, time-consuming, and generally can only be performed by outside laboratories. This confirmatory test is generally not useful in the emergency department, but has a role in cases of pediatric exposures, research, or occupational drug testing.     One of the limitations of a urine drug screen are the false-positive results from the interference of other drugs with the immunoassay, many of which are from structural similarities. Diphenhydramine and quetiapine commonly cause a false-positive for tricyclic antidepressants (TCA).                                TCA, left; diphenhydramine, center; quetiapine, right.   The specificity for phencyclidine (PCP) immunoassays is generally poor and false-positives may result from dextromethorphan, venlafaxine, tramadol, ketamine, and diphenhydramine.                                   PCP, left; dextromethorphan, center; venlafaxine, right.   The amphetamine/methamphetamine screen has many false-positives, including bupropion (Wellbutrin), dextroamphetamine (Adderall), methylphenidate (Ritalin), promethazine (Phenergan), pseudoephedrine, trazodone...
Source: The Tox Cave - Category: Emergency Medicine Tags: Blog Posts Source Type: blogs