What factors might explain higher sensitivity of urine for detection of buprenorphine when compared to oral fluid?
The detection window of buprenorphine is presumably longer in urine; the timing of drugs in oral fluid is similar to plasma and therefore less indicative of remote use. Also, concentrations of oral fluid norbuprenorphine are typically much lower than oral fluid buprenorphine, and the buprenorphine and norbuprenorphine glucuronide metabolites are not present in oral fluid.
Ransohoff JR, Petrides AK, Piscitello GJ, Flood JG, Melanson SEF. Urine is superior to oral fluid for detecting buprenorphine compliance in patients undergoing treatment for opioid addiction. Drug Alcohol Depend. 2019 Oct 1;203:8-12. doi: 10.1016/j.drugalcdep.2019.06.015. Epub 2019 Aug 1. PMID: 31394416