Can a threshold for 11-nor-9-carboxy-Δ
A 100 μgL or higher concentration of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH) in blood serum is generally assumed to be associated with regular andor heavy use of cannabis. At present, determination of the extent of cannabis use by means of the concentration of THC-COOH in hair has not been assessed. Therefore, we aimed at establishing a threshold for THC-COOH concentrations in hair to prove frequent consumption by comparing THC-COOH concentrations in 129 corresponding serum and hair samples, respectively. The concentration of THC-COOH in the serum was analyzed by gas chromatography-mass spectrometry and in the hair by liquid chromatography-tandem mass spectrometry. Data were statistically evaluated using receiver operating characteristic curves and contingency tables. Our results suggest that a THC-COOH concentration of ≥4.2 pgmg in hair was always accompanied by a THC-COOH concentration of at least 100 μgL in blood serum. Should this be confirmed by further studies of a larger study population, a hair concentration of 4.2 pgmg THC-COOH can be set as a threshold to predict regular andor heavy consumption of cannabis even if no corresponding blood sample is available for analysis.