Why Perform an Alcohol Test Before a Drug Test?
There are reasons why you perform an alcohol test before a drug test. Students who receive training to be Breath Alcohol Technicians and Specimen Collectors are taught that if an employee is to take both a drug test and an alcohol test that the alcohol test must be performed first. Students are told that the reason for this is that alcohol levels decline rapidly, and if the employee has alcohol in their system, delaying the alcohol test may create a lower test result. The delay could even turn what could be a “positive” result of .020 or greater into a negative result of less than .020. (Note that DOT never uses the term “positive” to describe an alcohol test result, but always refers to the threshold levels of .020 or greater or .040 or greater.)
What specifically is the impact of delaying the alcohol test when a person has alcohol in their system? We have adapted a chart that DOT created to project alcohol levels if the interval between screening and confirmation tests was increased. The chart assumes that an individual metabolizes alcohol to lower alcohol concentration by 0.01 to 0.02 an hour; we typically use an average rate of decline of .015 BAC per hour.
|Declining Alcohol Levels Over Time|
|Initial Alcohol Level||.06||.05||.04||.03|
|Delay||Predicted Result After Delay|
|20 minutes||.053 – .056||.043 – .046||.033 – 036||.023 – .026|
|30 minutes||.050 – .055||.040 – .045||.030 – .035||.020 – .025|
|40 minutes||.046 – 053||.036 – .043||.026 – .033||<.020 – .023|
|60 minutes||.040 – .050||.030 – .040||.020 – .030||<.020 -.020|
|120 minutes||.020 – .040||<.020 – .030||<.020 – .020||<.020|
Bolded results are considered to be negative (less than .020) for DOT alcohol testing.
The chart shows that a low alcohol level of .030 may decrease to below .020 if the test is delayed by more than 30 minutes. Granted, a typical specimen collection doesn’t take 30 minutes to complete. However if there is any complication in collecting the specimen – shy bladder, temp out of range, etc. – then the collection process could easily go beyond 30 minutes. And you could expect that an employee who has been drinking will be glad to do anything they can to delay the alcohol test. The longer the employee can delay the alcohol test, the lower the alcohol test result will be.
The chart projects results for the initial, or screening, test. The DOT protocol requires a 15 minute wait before performing the confirmation test. Therefore the projections for confirmation test results will be even lower, and will increase the possibility of the confirmation test being negative. And in the DOT protocol, the confirmation test is the final result. If a screening test is positive and the confirmation test is negative, the test is officially a negative result.
And that’s the long version of why you perform an alcohol test before a drug test.