Drug Detection Cutoff Values

Cutoff concentration for buprenorphine, 1.0 mL 6Cutoff ratio for buprenorphine/creatinlne,0.1 mg/mol. ever, cutoff concentrations suffer from the physiological disadvantage that abusers can and do drink plenty of water to dilute urine drug concentra-tions below the critical cutoff value, a manipulative polydypsia (this is hardly a new observation). Although, of course, false-positive results are to be avoided, there is also a pressure to avoid false-negative re-sults. To compensate for dilution, we have used a drug/creatinine ratio in examining buprenorphine misuse in Glasgow, Scotland (2). As can be seen from Table 1, using a urine concentra-tion cutoff of 1 mg/L for the drug buprenorphine, we would have re-ported six of these nine urine samples as negative; on using the ratio of bu-prenorphine/creatinine of 0.1 mg/mol, we would class them all as positive-half the samples being double, or much more, than the cutoff value. We applied the ratio in cases that were equivocal or negative by the concen-tration cutoff approach. We based our experience on several hundred sam-ples received from buprenorphine abusers. At the time of the original report (2), the incidence of buprenor-phine use in our addict population was>40%. The use of urine drug/urine creati-nine ratios need be no less generous in their setting to avoid false-positive re-sults than the concentration cutoff but would enhance the objectivity with which a result could be viewed. As an approach for routine drug screening, this may merit more intensive inves-tigation