Are the tests for intoxification reliable?

The successful prosecution of a DUI is dependent on the accuracy of the battery of tests that law enforcement officials use to determine intoxication in drivers.  Prosecutors must prove beyond a reasonable doubt that the accused’s blood alcohol content (BAC) was above a specific, legally mandated limit, and their impaired driving could not be attributed to factors other than intoxication with alcohol. The empirical measurements provided by standardized testing employed by law enforcement officials are heavily relied upon to secure prosecution.

However, the reliability and accuracy of these tests are the subjects of constant dispute among law enforcement, government officials, medical and technical experts and defense attorneys.  The previous testing standard was the Field Sobriety Test (FST), which was employed by the police officer at the site where the suspect was initially pulled over.  These tests relied on the officer’s subjective observations of the suspect while they were asked to perform a series of physical tasks meant to evaluate their fine motor skills, balance and other skills that may be impaired by consumption of alcohol.

These tests fell out of favor when it was discovered that they were extremely unreliable in testing the true level of intoxication (or lack thereof) of the suspect.  Some studies found that up to half of completely sober FST participants in ideal conditions (even surface, well-lit, etc.) would be found to be impaired based on the standards of the test.  Presently, officers may ask someone suspected of drunk driving to perform an FST to provide justification for further chemical testing, but the results of the FST would likely be insufficient to secure a DUI conviction.

The current standard of intoxication testing is chemical testing.  These tests are performed with an examination of a biological sample taken from the suspect – usually breath, blood or urine.  Using medical grade equipment, law enforcement officials can determine a suspect’s BAC as a percentage of alcohol by volume or by mass of blood.

While more scientific and objective than FSTs, the reliability of chemical tests has also been challenged.  Breathalyzers in particular are the subject of scrutiny, as they are the most widely conducted of the chemical tests but also possess the most potential for error.  Many factors can contribute to an erroneous breathalyzer reading, including miscalibration of the device, improper administration of the test by non-medical personnel, improper assumptions of blood-to-breath ratio inherent in the device or certain characteristics of the testee such as age, gender, pre-existing medical conditions and other considerations.

Blood tests are considered to be the most reliable test of BAC currently available.  Unfortunately, these tests require administration by licensed medical professionals and special equipment that most police stations do not have readily available.  They are also much more intrusive for the suspect.

Posted in: DUI