An evaluation of the diagnostic accuracy of liquid chromatography-tandem mass spectrometry versus immunoassay drug testing in pain patients.

Background: Immunoassay screening is used by pain physicians to determine compliance with controlled substances. Because clinical use of pain medications is different from illicit drug use, there is a need to evaluate the level of diagnostic accuracy of this procedure for the pain patient.

Objective: To compare the results of automated screening by immunoassay with analysis by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) in identifying pain patients using illicit drugs and pain patients excreting low concentrations of their prescribed medications.

Study Design: A diagnostic accuracy study.

Methods: Urine samples from 4,200 pain patients were tested by immunoassay and LC-MS/MS for the following drugs and metabolites: Amphetamine, Methamphetamine, Alpha-hydroxyalprazolam, Lorazepam, Nordiazepam, Oxazepam, Temazepam, Cannabinoids, Cocaine, Methadone, Methadone Metabolite, Codeine, Hydrocodone, Hydromorphone, Morphine, Propoxyphene, and Norpropoxyphene.

Results: In a number of patients negative immunoassay findings were superseded by positive results on analysis by Mass Spectrometry. These were termed false negative results. The greatest failures were for the benzodiazepines (28%) and for cocaine (50%).

Limitations: The study was limited by the lack of complete demographics for the cohort and because only one immunoassay diagnostic product was used. It was also limited because not all drugs react the same in the immunoassay.

Conclusions: We show that in general, immunoassay screening results are accurate, although as shown in this study there are many false negative observations. The use of LC-MS/MS technology significantly decreases the number of false negative results.