Defeating Retrograde Extrapolation Math in Arizona DUI Cases
If the police pulled you over on suspicion of a DUI but delayed drawing your blood for two, three, or even four hours, prosecutors run into a major legal problem. Under Arizona law, the state must prove your Blood Alcohol Content (BAC) was above the legal limit at the time you were driving, not hours later at a police station or hospital.
To bridge this time gap, the state's prosecution team relies on a toxicologist to perform a mathematical calculation known as retrograde extrapolation. In my 42 years of criminal defense practice in Phoenix, I have successfully exposed this practice for what it truly is: a highly flawed scientific guess.
The Fatal Flaws of DUI Back-Calculation Math
Retrograde extrapolation is a formula that attempts to guess your past BAC by counting backward from your later blood test. To make this math work, the state's expert must make a massive, dangerous assumption: that your body was already completely done absorbing the alcohol while you were driving.
In the real world of human biology, everyone's body processes alcohol differently. The math guess completely falls apart if your body was still in the absorption phase when you were stopped. Factors that ruin the accuracy of this calculation include:
- The Timing of Your Last Drink: If you drank shortly before driving, your BAC may have been very low while driving, but continued to rise after the police stopped you.
- Food in Your Stomach: Having a recent meal significantly slows down how fast your body absorbs alcohol, making back-calculation math completely unreliable.
- Individual Metabolism: Your unique weight, gender, health, and metabolic rate mean a generic math formula cannot accurately predict your personal biological history.
Our Defense Strategy to Exclude the State's Guesswork
We do not allow the state to convict you based on a generic mathematical formula. Our defense team aggressively attacks the scientific foundation of the toxicologist's report.
We meticulously cross-examine the state's witnesses to prove they lack the critical personal facts—such as the exact timing of your food and drink consumption—needed to make an accurate calculation. By demonstrating that the toxicologist's math is built on assumptions rather than hard facts, we can argue to the judge that the retrograde extrapolation results are unscientific, speculative, and should be entirely suppressed from your trial.
Don't Let a Flawed Math Guess Decide Your Future.
Put 42 years of aggressive, local legal experience in your corner. Contact Brian DiPietro Law, PLLC today at 623-242-2655 to schedule a free, confidential review of your case.
Put 42 years of aggressive, local legal experience in your corner. Contact Brian DiPietro Law, PLLC today at 623-242-2655 to schedule a free, confidential review of your case.
"Along with fighting back-calculation math, we also investigate if the state used Expired Blood Vials & Fermentation to artificially raise your BAC."
