DUI attorneys and people who have been arrested call me and sometimes ask: What happens when there is a DUI arrest, a .000 breath test, followed by a urine screen that is positive for drugs? Here is the answer. We use a toxicologist to testify about the limitations of urinalysis in the following fashion:

A urine drug screen takes place in a laboratory setting and involves multiple chemists and technicians. The process entails a battery of tests over the course of several days utilizing different instruments that represent a comprehensive examination for controlled substances. These tests include the “immunoassay presumptive test,” the “thin layer chromatography test,” the “gas chromatography test” and “mass spectrometry.” Some of these tests are “quantitative” which reveal concentration levels.

However, in a urine test, the results are always reported in a “qualitative” fashion. (Meaning that the results are reported in such a way that they are limited only to confirm the presence or absence of a drug.) The reason for this is quite legitimate since concentrations detected in urine do not correlate with concentrations found in the blood. Thus, urine concentration levels have no meaning in and of themselves since they represent a number related to what is found merely in the urine and not in the bloodstream. (And of course, it is only what is found in the bloodstream that directly relates to the issue of impairment at the time of driving.)

Usually, the State’s toxicologist can only testify that while the presence of a controlled substance was detected in the urine sample, it is impossible to determine based on this method of testing whether a driver was actually feeling the effects of that substance at the time he was operating the vehicle. Usually, the State’s expert witness will also have to admit that such uncertainty is due to the length of time that it takes for most prescription and illegal drugs to be processed or “eliminated” from the human body.