Interpreting urinary buprenorphine and norbuprenorphine levels
| Total urinary buprenorphine (ng/mL)a | Total urinary norbuprenorphine (ng/mL)a | N:B ratiob | Differential or likely diagnosis | |
|---|---|---|---|---|
| Scenario 1 | > 20 | > 45 | Usually > 0.26 | Recent dosing of at least some buprenorphine |
| Scenario 2 | Low, ≤ 20c | Low, ≤ 45c | Usually > 0.26 | Regular recent dosing Dosing at low levels Use of a CYP3A4-inducer Increased time since last dose Dilute urine |
| Scenario 3 | Positive, but low | Negative or very low | < 1 (may be 0) | Recent (within hours) dosing of buprenorphine for first time in days |
| Scenario 4 | High, usually > 700 | Negative | 0 | Buprenorphine spiking and no recent dosing |
| Scenario 5 | High, usually > 700 | Positive | < 0.26 | Probable buprenorphine spiking, likely recent dosing if norbuprenorphine level is not low Possible regular dosing when N:B ratio > 0.02 but < 0.26 |
↵a Total urinary levels listed here include the parent compound and the glucoronidated form (eg, total buprenorphine = free buprenorphine + buprenorphine- 3-glucoronide) achieved after laboratory hydrolysis.
↵b Some studies suggest using an N:B ratio of 0.02 as a threshold for identifying urine spiked with unconsumed buprenorphine. Using a more sensitive threshold of 0.26 keeps a broader differential.
↵c Some studies consider values < 100 ng/mL to be low.
CYP3A4 = hepatic cytochrome P450 3A4; N:B ratio = ratio of norbuprenorphine to buprenorphine