Blood for alcohol; spit for drugs: Challenging DUI tests

Police can’t say they don’t have support from lawmakers in their efforts to combat drunk or drugged driving. Legislatures in states across the country, including here in Tennessee, have passed laws that allow authorities to conduct scientific tests to try to prove when someone is actually under the influence of an impairing substance.

As we have noted in the past, that doesn’t mean police always have a clean shot at obtaining convictions with this kind of evidence. Supporting drunk driving charges based on blood or breath tests depends on being able to show the tests are accurate. That means they have to have been performed with properly calibrated equipment and following protocols that assure the integrity of the results. It doesn’t always happen.

It’s one thing to use blood test results as evidence for drunk driving cases. It is a generally accepted under law that if a blood tests shows you have an alcohol content of 0.08 percent or higher, you are considered impaired. And breath test results from the field are widely accepted as an acceptable way for authorities to establish probable cause to make an arrest.

Field-testing to show drugged impairment is a murkier issue, which has led some states to consider allowing police to use portable saliva tests. As this is written, 14 states permit so-called oral fluid testing to detect driving under the impairment of drugs, and two others have legislation pending. Tennessee is one of them.

One tool that seems quite popular with police is the German-developed Drager DrugTest 5000. Officials say the spit-testing device works much like a breath test and shows promise in being able to detect when a person has been recently using marijuana and perhaps some other drugs.

However, as one recent report by the Governors Highway Safety Association observes, there’s still the issue that no scientific consensus of a relation between drug concentrations in subjects and impairment. The GHSA says a more definitive answer to that question is needed.

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