Can a high BAC reading be wrong in Arizona?

The Whole Case Is One Number

In most Arizona DUIs the State’s case is a single BAC result. Undermine the number and you undermine the case.

Arizona can charge DUI two ways: impairment (A.R.S. 28-1381(A)(1)) and being at or above 0.08 (A.R.S. 28-1381(A)(2)). The “per se” 0.08 charge rests entirely on the reported number, so if the number is unreliable, the charge is in trouble.

People treat a breath or blood result as a fact. It is not, it is a scientific estimate produced by machines, chemicals, and people, every one of which introduces error. A forensic toxicologist is the expert who takes that estimate apart and shows the jury how much doubt is baked into it.

The Rising-BAC (Absorption) Defense

You are tested after driving, but the law cares about your level while driving. Those can be very different.

Alcohol is not in your blood instantly. After your last drink it keeps absorbing for 30 minutes to a couple of hours, so your BAC rises, peaks, and then falls. The test happens well after the stop, sometimes an hour or more later, meaning your BAC at the machine can be higher than it was behind the wheel.

If you were still absorbing, a 0.09 at the station could have been a lawful 0.07 while you were actually driving. A forensic toxicologist reconstructs your absorption and elimination curve from your drinking timeline, body weight, food, and the time gap, a process called retrograde extrapolation, to show your true level at the relevant moment.

The State uses retrograde extrapolation too, but it relies on assumptions that frequently do not fit real people. We expose those assumptions and offer the alternative the science actually supports.

What a Toxicologist Challenges

Beyond rising BAC, a toxicologist audits every scientific link in the chain.

A forensic toxicology review typically targets:

• Rising BAC / absorption, that your level was lower while driving than at the test.
• Retrograde extrapolation errors, the flawed assumptions in the State’s back-calculation.
• Machine and lab error, calibration, maintenance, and analytical problems (see our breath and blood guides).
• Physiological variables, how your body, health, and diet affect the reading (see medical defenses).
• Impairment vs. number, whether the alleged level actually proves you were impaired.

Each is reasonable doubt. Layered together, they can collapse a case that looked airtight on the police report.

Arizona BAC: The Numbers That Decide the Case

These thresholds drive the charge and the mandatory penalties, and the science that produces them is exactly what a toxicologist attacks.

The BAC Thresholds (and What Each Triggers)

• 0.08–0.149, standard DUI (A.R.S. 28-1381(A)(2)), min 10 days jail (9 suspendable).
• 0.15–0.199, Extreme DUI (A.R.S. 28-1382), min 30 days jail, mandatory interlock.
• 0.20+, Super Extreme DUI, min 45 days jail, higher fines.
• 0.04+, DUI for a commercial (CDL) driver.
• Any amount, drivers under 21 (zero tolerance) and drug DUI (A.R.S. 28-1381(A)(3)).

The Alcohol-Absorption Facts We Use

• Alcohol keeps absorbing 30 minutes to 2 hours after your last drink, your BAC is often still rising.
• The body eliminates alcohol at roughly 0.015 per hour, so timing changes the number.
• The test is usually taken an hour or more after driving, not while you drove.
• Food, body weight, sex, and drinking pace all shift the curve, and break the State’s assumptions.
• Retrograde extrapolation is only as good as those assumptions, which rarely fit a real person.

From a Bad Number to a Winnable Case

A toxicology challenge changes the leverage, and often the outcome.

When we retain a qualified toxicologist, the prosecutor knows the number will be contested in front of a jury by a credentialed scientist. That regularly produces reduced charges, dismissals, or acquittals, and it strengthens every negotiation.

This is one discipline in a full DUI defense. Explore the rest in our Top 10 DUI defenses, or start with our Phoenix DUI defense. Call 623-321-4699, 24/7.