Criteria for identifying new cocaine use: Presence of cocaine in urine

Methodology was developed to distinguish positive urine specimens due to New Use of cocaine from those due to Carryover in treatment subjects (NIDA Research Monograph 162:143-144,1996). One criteria for identifying a positive urine as Carryover required that the concentration of benzoylecognine (BZE) decrease by at least 50% compared a specimen collected at least 48 hr earlier. To test this criteria we determined concentrations of BZE (immunoassay) and cocaine (GC/MS) in nearly 2500 urine specimens collected from 62 subjects in a cocaine treatment trial. We systematically varied the required BZE decrease in the New Use criteria (50, 25, 15, 5%) and compared New Uses to the presence of cocaine. Because the half-life of cocaine (0.75 - 1 hr.) is shorter than that of BZE (6 - 8 hr), cocaine should be present more frequently in positive specimens identified as New Use than as Carry-over. Concentrations (mean ± SEM) were 1424 ± 137 (range 0-112025) ng/mL cocaine and - 31601 ± 1884 (range 0-1900000) ng/mL BZE. Cocaine tended to track BZE (mean r=0.42; p<.0001) but was lower in concentration and detectable in fewer specimens. Cocaine was present in 72 to 68% of New Use positives and in 26 to 48% of Carryover positives when the required decrease in BZE concentration was varied from 5 to 50%, respectively. The presence of cocaine generally supported the validity of the New Use Criteria.