Interpretation of urine quantitative 11-nor-delta-9 tetrahydrocannabinol-9-carboxylic acid to determine abstinence from marijuana smoking.

Verification of abstinence from cannabinoid use after initial identification requires documentation of falling quantitative levels of urinary 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) over an extended time period. We present a case in which normalization of quantitative urinary THC-COOH results to urinary creatinine is required to correctly interpret a series of quantitative levels and confirm abstinence from marijuana smoking.