Correlations and agreement between delta-9-tetrahydrocannabinol (THC) in blood plasma and timeline follow-back (TLFB)-assisted self-reported use of cannabis of patients with cannabis use disorder and psychotic illness attending the CapOpus randomized clinical trial
Version of Record online: 13 FEB 2012
© 2011 The Authors, Addiction © 2011 Society for the Study of Addiction
Volume 107, Issue 6, pages 1123–1131, June 2012
How to Cite
Hjorthøj, C. R., Fohlmann, A., Larsen, A.-M., Arendt, M. and Nordentoft, M. (2012), Correlations and agreement between delta-9-tetrahydrocannabinol (THC) in blood plasma and timeline follow-back (TLFB)-assisted self-reported use of cannabis of patients with cannabis use disorder and psychotic illness attending the CapOpus randomized clinical trial. Addiction, 107: 1123–1131. doi: 10.1111/j.1360-0443.2011.03757.x
- Issue online: 4 MAY 2012
- Version of Record online: 13 FEB 2012
- Accepted manuscript online: 9 DEC 2011 09:04AM EST
- Submitted 12 August 2011; initial review completed 21 September 2011; final version accepted 6 December 2011
- dual diagnosis;
- timeline follow-back;
Aims To assess correlations and agreement between timeline follow-back (TLFB)-assisted self-report and blood samples for cannabis use.
Design Secondary analysis of a randomized trial.
Setting Copenhagen, Denmark.
Participants One hundred and three patients from the CapOpus trial with cannabis use disorder and psychosis, providing 239 self-reports of cannabis use and 88 valid blood samples.
Measurements Delta-9-tetrahydrocannabinol (THC), 11-hydroxy-delta-9-tetrahydrocannabinol (11-OH-THC) and 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) detected in plasma using high-performance liquid chromatography with tandem mass spectrometry detection. Self-report of cannabis-use last month by TLFB. Pearson's r, sensitivity and specificity calculated as measures of correlation or agreement.
Findings Correlations were strong; r = 0.75 for number of days and r = 0.83 for number of standard joints in the preceding month when excluding outliers. Including outliers, coefficients were moderate to strong (r = 0.49). There were differences in subgroups, mainly inconsistent, depending on inclusion or exclusion of outliers. Sensitivity and specificity for TLFB detecting the presence or absence of cannabis use were 95.7% [95% confidence interval (CI) 88.0–99.1%) and 72.2% (95% CI 46.5–90.3%), respectively. Using 19 days as cut-off on TLFB, they were 94.3% (95% CI 86.0–98.4%) and 94.4% (95% CI 72.2–99.9%), respectively. Area under the receiver operating characteristic (ROC) curve was 0.96.
Conclusions Timeline follow-back (TLFB)-assisted self-report of cannabis use correlates highly with plasma-delta-9-tetrahydrocannabinol in patients with comorbid cannabis use disorder and psychosis. Sensitivity and specificity of timeline follow-back appear to be optimized with 19 days as the cut-off point. As such, timeline follow-back may be superior to analysis of blood when going beyond 19 days of recall.