[Urinary excretion of cannabis metabolites]

Urine testing is increasingly used to detect drug abuse, most commonly by easily performed immunological tests. There is large interpersonal variation in the excretion time of cannabinoids. Excretion times of up to 11 weeks have been demonstrated. In cases with a long excretion time a negative test result may be followed by a positive result without concomitant abuse. We describe a case where cannabinoid metabolites in urine were detected by a routine immunological method (Abbotts ADx) after 95 days of supervised abstinence. It is important that personnel evaluating test results have a thorough knowledge of possible pitfalls.