Validity of self-reported drug use in chronic pain patients

Previous researchers have reported that in psychiatric populations many patients provide incorrect self-report information on current drug use. Therefore, the purposes of the present study were to determine the percentage of chronic pain patients (CPPs) using illicit drugs (cannabis, cocaine), to determine the percentage of CPPs who provide incorrect self-report drug use information in the psychiatric examination, and to identify some variables that could help in identifying the CPP likely to provide an incorrect drug use history using drug urine toxicologies. DESIGN/SETTING/PARTICIPANTS/OUTCOME MEASURES: Two hundred seventy-four CPP consecutive admissions to a pain facility were psychiatrically examined according to criteria in the Diagnostic and statistical manual of mental disorders (3rd ed., rev; DSM-III-R), with special emphasis on all current drug use. Immediately after the psychiatric examination, all CPPs were asked to consent to urine toxicology. Urine was tested for benzodiazepines, opioids, tricyclics, propoxyphene, cannabinoids, barbiturates, amphetamines, methadone, methaqualone, phencyclidine, alcohol, and cocaine. CPPs were then segregated into three groups: negative toxicology, positive toxicology but concordant with self-report of current drug use, and positive toxicology discordant with self-report of current drug use. These groups were statistically compared with each other with regard to age, gender, race, workers' compensation status, and prevalence of individual DSM-III-R psychoactive substance use disorders. Sensitivities were also calculated for two conditions: accuracy of toxicology and accuracy of self-report.

Toxicologies were obtained from 226 (82.5%) of the CPPs. Toxicologies were negative in 121 (53.5%) and positive in 105 (46.5%) of the CPPs. Of the 226 CPPs, 8.4% had illicit drugs in the urine (6.2% cannabis, 2.2% cocaine). Twenty (8.8%) of the CPPs provided incorrect self-report information about current drug use, the incorrect information most frequently about illicit drugs. Drug urine toxicology sensitivity results indicated that a significant percentage of CPPs was claiming to be taking a drug but was not taking it or taking it incorrectly. The psychiatric examination drug self-report sensitivity results indicated that a significant percentage of CPPs was withholding or providing incorrect information on current drug use. Lowest self-report sensitivity results were in reference to illicit drugs. CPPs who were more likely to provide incorrect psychiatric examination self-report information about current drug use were more likely to be younger, to be a workers' compensation CPP, and to have been assigned a DSM-III-R diagnosis of polysubstance abuse in remission.

A significant percentage of CPPs appears to provide incorrect information on current illicit drug use. Urine toxicology studies may have a place in the identification of drugs for which incorrect information may be provided by CPPs. There are many possible reasons, such as assay error, that could lead to apparent misinformation. In the clinical setting, these possibilities should be considered if urine toxicology results appear to be incongruent with psychiatric examination drug use self-report.