With the increasing number of marijuana users day by day, the need for the drug test became important. With the evolution of self test kits which are easy to use, people are using them on a wide range. While using these kind of test kits it is important to know the cutoff points and when the test will be called as positive. Then only we can come to conclusions relating to the test.
For most of the laboratory tests and the instant tests like the blood, urine, saliva and the hair tests, 50 nanograms per ml is defined as a presumptive positive by SAMHSA. In the beginning this number used to be 20ng/ml, but resulted in too many false positives and hence it is increased to 100ng/ml. However, again in 1995, the cutoff is lowered back down to 50ng/ml since it was believed that excessive drinking of water could bring the metabolites in urine below 100ng/ml.
For this cutoff, if the specimen screens non negative for THC, then it is sent through a Gas chromatograph/Mass Spectrometer(GC/MS) for specific metabolite tripping the immunoassy screening. For that the cut off is set at 15 ng/ml, and it is used as a confirmation for a positive on the drug test.
In a simpler way, the initial screening cutoff level is 50 ng/ml and the GC/MS cutoff is 15 ng/ml. The elimination half life for the drug marijuana ranges from 14-38 hours. At the initial cutoff the regular user will remain positive for 7-30 days after cessation and for confirmation level the daily user will be positive as long as 15 weeks.