Those instant strip drug tests are quite accurate nearly 95-97%. They include a control line to make sure the test hasn't gone bad from age or heat exposure and such. If you want to be sure use 2 strips. Also, most of these strips are set to detect levels of THC above 50ng/ml, which is what most lab tests are set for. However, some (very few) employers use a more stringent 20ng/ml cutoff level for THC. So, if the lab is using the same threshold that the instant strips are using, then those strips are very accurate.