The concept of cut-off levels is a fundamental concept of drug and alcohol testing with which every professional should be familiar. A cut-off level establishes the point at which results are considered positive. A working knowledge of cut-off levels is particularly important in alcohol testing, where the test device usually does not report the result as “positive” or “negative,” but is more likely to give a numerical result. The burden is on the operator to correctly interpret that result as “positive” or “negative.”
The lay person might think that the only result that can be considered negative is 0.000, and any result that is greater than zero should indicate a positive test- for example, 0.001. However, the fact is that cut-off levels are typically set considerably higher than zero to reduce the number of false positive results.
In 1994 the U.S. Department of Transportation (DOT) chose 0.020 as the cut-off for a positive alcohol test. The 0.020 cut-off level has become the standard in the U.S. for workplace alcohol testing, as well as other testing programs that want to rely on an industry-standard cut-off level.
Because the ramifications of positive alcohol tests are usually less severe in substance abuse treatment programs compared to workplace testing, it may be appropriate for treatment programs to use 0.010 as a cut-off level when using an Alco-Sensor instrument. However, a 0.010 cut-off level may not be appropriate when using an inexpensive alcohol testing device using semi-conductor technology that is not specific for alcohol.
Defining a cut-off level for positive alcohol test results also defines negative results as any result lower than the cut-off level. For example a 0.020 cut-off level means every result from 0.000 to 0.019 is a negative test. A 0.010 cut-off level means 0.000 to 0.009 is negative. Classifying non-zero alcohol test results as negative- for example, 0.005, .010, 0.019, etc. – might seem counter-intuitive to the lay person, but it is never-the-less correct.
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