Why is the result from a THC-Quantitative screen so much higher than the THC result from the GC/MS on the same sample?
The THC in marijuana is broken down into at least five different metabolites, which are excreted in the urine. The THC-Quant test is performed by immunoassay and is sensitive to all the marijuana metabolites, whereas the GC/MS test is specific for only the most abundant metabolite, THCC. The rule of thumb is that the level measured by GC/MS should be about one third of the level measured by immunoassay.
