Urine drug tests (UDTs) are broken down into two separate categories, screening UDTs and confirmatory UDTs. Screening UDTs are immunoassay tests involving antibody technology. Screening UDTs have a higher risk of false positive and false negative results compared with confirmatory UDTs that are done by gas chromatography and mass spectrometry (GC/MS). Screening UDTs are inexpensive and yield results within minutes. Confirmatory UTDs are send-outs, are expensive, and it usally takes several days to get the results back.
Screening UTDs test for commonly abused substances such as cannabis, methamphetamine/amphetamine, cocaine, oxycodone, benzodiazepines, barbituates, opiates, and PCP. False positives can occur. For example, a false positive for amphetamine can occur because of the use of bupropion, pseudoephedrine, and over the counter Vicks decongestants which contain l-methamphetamine, not d-methamphetamine, the abused isomer. False positives for benzodiazepines can be caused by sertraline which is a common drug to treat anxiety or mild depression. Medications that can cause positive PCP (phencyclidine) results include dextromethorphan, carbamazepine, TCAs (tricyclic antidepressants) like Elavil, and venladfaxine.
To rule out false positives, urine is often sent to a lab for quantitative analysis by GC/MS.
Opiates, substances derived from opium plants like codeine or morphine. False positives for opiates can occur with opioids (synthetic or semisynthetic such as fentanyl, oxycodone, or hydromorphone) such as hydromorphone, naloxone, naltrexone, trazodone, or even a blood pressure medication, labetolol.