Can a threshold for 11‐nor‐9‐carboxy‐Δ⁹ ‐tetrahydrocannabinol in hair be derived when its respective concentration in blood serum indicates regular use?

Abstract

A 100 μg/L or higher concentration of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH) in blood serum is generally assumed to be associated with regular and/or 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 pg/mg in hair was always accompanied by a THC-COOH concentration of at least 100 μg/L in blood serum. Should this be confirmed by further studies of a larger study population, a hair concentration of 4.2 pg/mg THC-COOH can be set as a threshold to predict regular and/or heavy consumption of cannabis even if no corresponding blood sample is available for analysis.

Positive THC‐COOH findings in hair samples negative for THC

“…In a second step, THC positive cases can be further analyzed for 11‐OH‐THC and THC‐COOH to proof active consumption. In addition, the concentration of THC‐COOH in hair samples can be used as an indicator of regular and/or heavy consumption of cannabis …”

“…An effective washing procedure should also be performed prior to further sample processing and wash residues should be kept aside if further inconsistencies will be apparent. In cases of suspected actual cannabis use, the combined determination of THC‐COOH in both hair and blood/serum samples seems to be a more appropriate method to identify heavy users of cannabinoids than the isolated viewing …”