Testing for secondhand marijuana exposure

Current drug tests can detect large amounts of the psychoactive marijuana component tetrahydrocannabinol (THC) and its metabolites in urine. That's sufficient when testing whether a potential employee or professional athlete has used the drug. But in the case of secondhand marijuana smoke, the levels of these substances in the urine are too low to be flagged, so it's difficult to assess whether this type of exposure could cause harmful health effects. As a first step toward investigating the effect of secondhand marijuana smoke exposure, Binnian Wei and colleagues at the U.S. Centers for Disease Control and Prevention sought to develop a more sensitive urine test for cannabinoids.

The researchers combined ultrahigh performance liquid chromatography and tandem mass spectrometry with positive electrospray ionization mode to develop a reliable, fast and accurate method to test for THC and its metabolites. The approach is 10 to 100 times more sensitive than current methods. In laboratory tests, the method detected the substances at levels approximating those that would be in the urine of someone exposed to secondhand marijuana smoke. Because the method is semi-automated, it could be used for large-scale population studies.