Review Question - QID 102945

This vignette describes a patient involved in a motor vehicle accident secondary to potential substance use. The "gold standard" confirmatory test for substance use is gas chromatography / mass spectrometry (GC/MS).

Urine drug testing is often employed in the forensic setting. However, screening and confirmatory testing distinctions exist. GC/MS remains the current “gold standard” for confirmation testing. It employs GC to separate the analytes in a specimen, and the highly specific and sensitive MS to identify specific molecular structures of the drug and metabolites. This technique allows both qualitative and quantitative measurements to be obtained. Clinically, GC/MS can be used to identify presence of drugs that are not reliably detected by screening modalities.

Walsh et al. collected drug and alcohol test data for drivers brought to a level-1 trauma ED. In the methodology, they specify that GC/MS is used to minimize false-positive results from initial urine drug screening tests. Sadly, they found that although more than half of 108 drivers had presence of multiple drugs in their bodies, less than half of them were referred for drug counseling.

Owen et al. review the literature for best practices regarding urine drug testing, particularly in the setting of chronic pain management. They caution that urine drug screens must be followed by confirmatory testing in patients at high risk for multiple substance use. This is because screening modalities often cannot distinguish drugs from the same class. GC/MS allows for specific metabolites to be identified and quantified, allowing for more rigorous assessment of compliance.

Incorrect Answers:
Answer 1: Polymerase chain reaction is a molecular biology technique used to amplify DNA sequences. It is not used in drug testing.
Answer 2: Urine immunoassay is a screening test, not a confirmatory test.
Answer 3: Western blot is molecular biology technique used to confirm the presence of a specific protein or antibody after an immunoassay. It is not employed in substance use testing.
Answer 5: Breath alcohol tests are used to detect blood alcohol levels based on exhaled alcohol. It is used to screen for alcohol use.