One of the key concepts within drug testing is the application of a cut-off level. This is the point which segregates a test result as being either positive or negative.
For drug screening tests, a cut-off is chosen that will optimise drug detection but minimise the number of false positive results. It is important to note that a negative sample doesn’t mean that it is drug free; it might contain a drug at a concentration that is lower than the defined cut-off.
If a drug test is reported as screen positive or presumptive positive, this merely shows a response, which is usually because a drug is present. It cannot show how much drug was taken or be correlated to any degree of impairment. As this is a screening tool, all presumptive positives require a confirmation test.
Figure 1: A visual representation of a cut-off level and window of detection.
Finding a cut-off level
The cut-off levels for our the majority of our products are available within the Instructions For Use. You can find these on our product pages within the resources tab.
Our laboratory cut-off levels are detailed within our Technical Specifications.