Carolina Criminal Defense & DUI Lawyer UpdatesIn North Carolina impaired driving cases where retrograde extrapolation becomes relevant, chemical testing is often separated from the driving event by significant delay. 
This is most commonly seen in serious vehicular prosecutions where impaired driving serves as a predicate offense, including collision investigations involving injury or death, where scene management, medical transport, search warrant procedures, and hospital blood draws may delay specimen collection for three or more hours.
This timing gap can create an evidentiary question that prosecutors sometimes attempt to address using a technique known as retrograde extrapolation, a calculation intended to estimate a prior blood alcohol concentration based on a later chemical test.
Retrograde extrapolation relies not on statutory fiat but on biology. Whether it carries scientifically reliable, relevant evidentiary value in any individual case depends on the science of alcohol absorption, distribution, and elimination. Put simply, contrary to the assertions of some, it’s neither clear-cut nor fait accompli.
a range of charges depending on the circumstances. Two of the most serious offenses are Felony Death by Vehicle and Second-Degree Murder.
technical procedures—such as chemical breath tests, blood alcohol analyses, and field sobriety testing—that lay jurors or even judges may not fully understand. An expert witness, properly qualified and admitted, can provide insight into such complex matters both for the prosecution and the defense.