The validity of drug use self-reports among hard core drug users in a household survey in Puerto Rico: comparison of survey responses of cocaine and heroin use with hair tests.

The extent to which underreporting of drug use in household surveys affects the validity of epidemiological studies of drug use disorders is largely unknown. We developed a list of known hard core drug users as part of a larger household study in Puerto Rico. The known drug users were recruited and interviewed with the same procedures used for the respondents selected through area-probability sampling. Upon completion of the interview, subjects were asked to provide a sample of scalp hair. A total of 78 hair specimens were collected from the known drug users. Hair specimens were screened for cocaine and heroin using radio immunoassay, and confirmed using gas chromatography/mass spectrometry. Using the cutoff of 0.2 ng/mg of hair, 93.2% of the hair specimens were classified positive for cocaine and 75.7% for heroin. With the hair test results as the gold-standard, we calculated specificity and sensitivity statistics as measures of the validity of self-reports. Self-reports of drug use in the past 3 months had a specificity of 78% or higher for both drugs. The sensitivity of self-reports was 69.6% for reports of recent cocaine use and 78.6% for reports of recent heroin use. Sensitivity increased with reports of use in more remote time periods, among subjects reporting DSM-IV drug disorder symptoms, and among those reporting use of both drugs. The results suggest that while drug reports of hard core drug users interviewed in household surveys might be more valid than those of the general population, there still remains considerable under-reporting.