Cut-Off Levels for Positive Alcohol Tests
One of the more frequent guidance we offer our customers is establishing cut-off levels for positive alcohol tests. It’s tempting for some users to regard any non-zero result as positive. After all, when a sober person blows into an Alco-Sensor breath alcohol instrument the result is always .000. Why not regard a result of .001, .002, .003, etc. as positive?
While it might make life a little simpler if one could treat any non-zero result as a positive alcohol test, there are several reasons why we do not recommend that users treat readings from .001 to .009 as positive tests.
First of all we point out what a tiny amount of alcohol that a reading from .001 to .009 represents. Picture a ruler marked in centimeters and millimeters. Now imagine that between each of the tiny millimeter lines there are 10 more lines. Those 10 imaginary lines between each millimeter on the ruler are the equivalent of the third digit of the Alco-Sensor. The imaginary lines ruler represent 100 micrometers; the third digit on the Alco-Sensor represents 1/1,000 BAC. So a reading between .001 and .009 is like trying to read one of the micrometer lines that is between the end of the ruler and the first millimeter line of the ruler.
Secondly, we point out that it is standard laboratory practice to establish a cut-off level to identify a positive test. For example, when laboratories test for drugs, they do not accept the presence of drugs at any level as a positive test. Instead, scientists establish cut-off levels that are high enough to have a high degree of confidence that the individual used the drug. Cut-off levels must also account for the margin of error inherent in every measuring device. A negative drug test result does not mean that the specimen contained zero drugs; it means that drugs were not present at or above the cut-off level established for that drug.
For workplace and other evidential testing applications we recommend using a 0.020 cut-off level; results of 0.019 and below are regarded as a negative test. This is the cut-off level established by the Department of Transportation (DOT) for workplace testing, and thus can be readily defended.
For substance abuse treatment programs and other non-evidential applications we are comfortable recommending a 0.010 cut-off level when using an Alco-Sensor. Results of .009 and below are treated as a negative test.
See our related article on zero tolerance alcohol testing for a more in depth discussion
Robert Martin says
My supervisor with 20 years of service at the railroad just had a random and had his last beer at midnight ! He had a random screening at 8AM. He blew a .025, fifteen minutes later he blew a .002 and was subsequently fired ! This is proof that some companies need to be enlightened to the science involved with determining what level of evidence is irrefutable and what should be ignored !
Jennie Lee-Pace says
Hi Robert. If the results of the confirmation test was in fact .002, this is considered a negative test by DOT standards. However the railroad company may have a different, more stringent (zero tolerance) policy.
Michael Roberts says
I had just used mouth wash not thinking after I had eaten egg salad. I blew a .01 and was told I failed the test after spending 20 min them trying to figure out the machine then they called my HR manager to let them know I failed. Then they where filling out paperwork and realized it was in fact a negative result bc it was at .01 not above .02. They stressed how sorry they where and called my HR manager back but then told me try and not use mouth wash before coming in. That part was my fault but their fault for not knowing how to use the machine and thinking a .01 was a positive result.
Jennie Lee-Pace says
Hello. We cannot stress enough the importance of getting proper training when using a breath alcohol device and knowing how to interpret test results. Using mouthwash just prior to a test can produce a reading of .01, but only if you use mouthwash within :15 of blowing into the breathalyzer. After :15 the alcohol from mouthwash will dissipate in the mouth and test results would be .000. The egg salad had nothing to do with the .01 result. Only alcohol is detected by the fuel cell. So if you used mouthwash more than :15 before blowing into the device, it is because other alcohol was detected in your breath.