title: 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.
abstract: OBJECTIVE
  To assess correlations and agreement between timeline follow-back (TLFB)-assisted self-report and blood samples for cannabis use.
  
  
  METHODS
  Secondary analysis of a randomized trial.
  
  
  METHODS
  Copenhagen, Denmark.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
authors.affiliation: Mental Health Centre Copenhagen and Faculty of Health Sciences, University of Copenhagen, Copenhagen NV, Denmark. carsten.rygaard.hjorthoej@regionh.dk
authors.forename: Carsten Rygaard
authors.initials: CR
authors.lastname: Hjorthøj
authors.forename: Allan
authors.initials: A
authors.lastname: Fohlmann
authors.forename: Anne-Mette
authors.initials: AM
authors.lastname: Larsen
authors.forename: Mikkel
authors.initials: M
authors.lastname: Arendt
authors.forename: Merete
authors.initials: M
authors.lastname: Nordentoft
mesh_terms: D015415:Biomarkers / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D013759:Dronabinol / Q000031:analogs & derivatives* / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000150:complications / Q000175:diagnosis*; D011618:Psychotic Disorders / Q000150:complications*; D012372:ROC Curve; D057566:Self Report; D015813:Substance Abuse Detection / Q000379:methods
chemical_list: D015415:Biomarkers; C001427:11-hydroxy-delta(9)-tetrahydrocannabinol; C016780:11-nor-delta(9)-tetrahydrocannabinol-9-carboxylic acid; D013759:Dronabinol; C025351:delta(9)-tetrahydrocannabinolic acid