Method used to estimate blood-alcohol level called "junk science"

Criticism is mounting against a method used in North Carolina and elsewhere to estimate blood-alcohol levels.

A method used by some prosecutors, including in North Carolina, to estimate the blood-alcohol level of alleged drunk drivers who are involved in collisions is coming under increasing scrutiny. The method, called retrograde extrapolation, attempts to estimate how much alcohol a driver had in his or her system at the time of a crash even if a blood test is not taken until hours after the actual accident. As WBAY News reports, while the method has been defended by prosecutors as a necessary tool against drunk driving, critics have decried the method as "junk science."

Retrograde extrapolation

Retrograde extrapolation is a forensic technique that tries to estimate what a defendant's blood-alcohol content (BAC) level would have been hours prior to a blood test actually having been taken. For example, in a recent case in New York a defendant registered a BAC level of 0.06 during a test taken four hours after a fatal crash in which he was involved. However, using retrograde extrapolation, prosecutors claimed his BAC level at the time of the crash would have been 0.12, above the state's legal limit of 0.08.

Defenders of retrograde extrapolation say its use discourages people who cause drunk driving accidents from fleeing the scene of an accident as a way of avoiding a blood-alcohol test. They also insist that the technique is important in order to get convictions for alleged drunk drivers.

"Junk science"

The technique, however, has plenty of critics and many states have restricted its use. In 2011, for example, the Nevada Supreme Court expressed misgivings about retrograde extrapolation. According to the Las Vegas Sun, the court placed severe restrictions on when the technique could be used in drunk driving cases, saying that retrograde extrapolation could risk prejudicing a jury against a defendant.

Among the problems with the technique is that it is difficult to verify whether a defendant's body was still absorbing or eliminating alcohol when a test was taken. Not knowing for certain when the body has started to eliminate alcohol from its system makes it extremely difficult to extrapolate how much alcohol was actually in that body at a specific time. Furthermore, critics point out that other factors, including gender, diet, drinking habits, and whether the defendant had experienced a traumatic event (such as a car accident) could all impact the rate at which alcohol is eliminated from the body.

DUI charges

Being charged with a DUI can be a frightening event. If convicted, a person could lose their license, be ordered to pay steep fines, or even face prison time. In some cases, driving restrictions may make it difficult to maintain one's employment and quality of life. If facing a DUI charge, a qualified criminal defense attorney should be contacted right away. An experienced attorney will be able to inform clients of what options they have and how best to handle these serious charges.