Temporal and gender trends in concordance of urine drug screens and self-reported use in cocaine treatment studies

Objectives: To describe temporal trends in concordance, sensitivity, and specificity and to explore demographic trends in concordance in two outpatient treatment studies for cocaine dependence.

Methods: We obtained 2229 urine drug screens from 129 individuals, along with accompanying self-use reports. Paired self-use reports and urine drug screens were considered concordant if the two measures of cocaine use were in agreement. The sensitivity and specificity of the self-use reports in predicting the urine drug screen was also estimated. To model concordance, sensitivity, and specificity as a function of time, generalized estimating equations were used. Demographic effects on concordance among subjects who achieved 100% concordance and subjects who achieved a recently proposed 70% concordance threshold were tested.

Results: Over the course of our studies, both sensitivity and concordance statistically decreased, yet specificity remained relatively constant. Median concordance for all subjects was 88%. Among all subjects, concordance varied significantly by gender, with females achieving significantly higher concordance than males (96% vs. 86%). Similarly, females were almost twice as likely to achieve 100% concordance as males (42% vs. 22%). Finally, 80% of participants achieved the 70% concordance threshold, and no differences among demographic groups with regards to the 70% concordance threshold were observed.

Conclusions: Temporal effects of concordance and sensitivity may have profound repercussions when using self-use reports to gauge efficacy of an experimental intervention. Furthermore, gender may differentially affect concordance. Finally, a substance abuse outcome measure that reliably combines objective and self-report data is promising, but further research is needed.