The Science Behind the Number
Breath & Blood Testing
The number on the report is not the end of the story.
Chemical test results look authoritative — a machine printed a number, a lab signed a report. But breath machines rest on population-average assumptions, and blood evidence depends on a long chain of human steps: the warrant, the draw, the tube, the storage, the lab. A failure at any link can be challenged.
The clock is already running. If you were served a suspension order, you have 30 days to request your MVD hearing under A.R.S. § 28-1385 — separate from any court date, and gone forever if you miss it.
First 24 Hours GuidePart One
Breath Testing: A Number Built on Assumptions
Evidentiary breath instruments like the Intoxilyzer 9000 use infrared spectroscopy to measure alcohol vapor in a breath sample — then convert that measurement into a blood-alcohol estimate using assumptions that are true on average and false for many individuals. The machine also depends on the operator following a strict protocol before you ever blow. Each assumption and each protocol step is a potential point of failure.
The Partition Ratio Assumption
Breath machines never measure blood. The Intoxilyzer 9000 measures alcohol in your breath and multiplies by a fixed 2100:1 'partition ratio' to estimate blood alcohol. Actual human ratios vary widely — roughly 1100:1 to 3200:1 — with body temperature, breathing pattern, and physiology. A person with a low true ratio can blow a number far above their real BAC.
Mouth-Alcohol Contamination
The machine assumes the sample comes from deep lung air. Residual alcohol in the mouth — from a recent drink, burping, acid reflux/GERD, dentures, or even some mouthwashes — produces falsely high readings because raw mouth alcohol never went through the 2100:1 dilution the math assumes.
The 15–20 Minute Deprivation Period
To guard against mouth alcohol, the operator must continuously observe you for a deprivation period (15 to 20 minutes depending on protocol) before the test — no drinking, eating, burping, vomiting, or foreign objects in the mouth. Officers who were driving, writing reports, or processing paperwork during the 'observation' did not comply. Logs and body-cam footage tell the truth.
Calibration & Maintenance Records
Every evidentiary breath machine must be periodically calibrated against known alcohol standards and maintained per the manufacturer and state regulations. Missed calibration checks, out-of-tolerance results, repair history, and expired standard solutions are all discoverable — and all undermine the number.
Radio-Frequency Interference
Police radios, cell phones, and transmitters near the instrument can interfere with its electronics. Machines carry RFI detectors, but detectors fail and protocols get ignored. Where the test occurred — a busy booking room full of radios — matters.
Why This Matters in Arizona
Arizona agencies have largely shifted from breath to blood — but breath tests still appear in many cases, especially as preliminary screens. If your case includes a breath number, every record above is discoverable.
Part Two
Blood Testing: Arizona’s Weapon of Choice
Arizona is predominantly a blood-draw state. Many agencies field their own police phlebotomists and obtain telephonic warrants within minutes. Blood is more accurate than breath — which is exactly why the chain of constitutional and scientific requirements around it matters so much. From the warrant to the gas chromatograph, here is where blood evidence breaks down.
No Warrant, No Consent
A blood draw is a search. Absent valid consent or true exigency, police need a warrant. Missouri v. McNeely held that alcohol dissipation alone is not an automatic exigency; Birchfield v. North Dakota confirmed blood tests are too intrusive to justify as a search incident to arrest. A draw that ignored these rules invites suppression of the result.
Unqualified Person, Unreasonable Draw
Since Schmerber v. California, blood must be drawn in a medically reasonable manner by qualified personnel. In Arizona, draws are often performed by police phlebotomists rather than hospital staff — their training records, certification currency, and draw-site conditions (the hood of a patrol car is not a clinic) are all fair game.
Gray-Top Tube Preservative Failures
Forensic blood goes into gray-top tubes containing sodium fluoride (an antimicrobial preservative) and potassium oxalate (an anticoagulant). Too little preservative, expired tubes, or inadequate mixing (the tube must be inverted repeatedly) lets microbes survive and the sample clot — both of which corrupt the result.
Fermentation: Alcohol Created in the Tube
If preservative fails and the sample sits warm — in a patrol car trunk, an evidence locker without refrigeration — Candida albicans and other microbes can ferment the blood's own sugars into new alcohol. The lab then measures alcohol that was never in your body. Storage temperature logs and delay between draw and analysis are critical evidence.
Chain of Custody Gaps
Every transfer — officer to evidence room, evidence room to lab courier, courier to analyst — must be documented. Missing signatures, unexplained delays, and mismatched seal numbers raise the question every juror understands: can the State prove this tube of blood is yours, untampered, and unaltered?
Headspace Gas Chromatography & Uncertainty
Labs measure blood alcohol by headspace gas chromatography: the vial is heated, vapor above the blood is sampled, and the instrument separates and quantifies compounds. It is sensitive but not infallible — co-eluting compounds, bad internal standards, pipetting errors, and carryover from prior samples all occur. Every measurement also carries a stated uncertainty range; a reported 0.082% with ±0.005 uncertainty may not prove the 0.08% element beyond a reasonable doubt.
The Constitutional Trilogy
Schmerber v. California (1966)
Blood draws are searches under the Fourth Amendment and must be performed reasonably, by qualified personnel, in a medically acceptable manner.
Missouri v. McNeely (2013)
Alcohol’s natural dissipation does not create an automatic exigency. Absent real case-specific urgency, police must get a warrant.
Birchfield v. North Dakota (2016)
Warrantless breath tests may follow a lawful arrest, but blood tests are too intrusive — and a state cannot make it a crime to refuse a warrantless blood draw.
The Rights That Protect You
Arizona’s implied-consent scheme gives the State leverage — but it gives you enforceable rights too. Knowing them, and acting inside the deadlines, is half the battle.
Your Right to an Independent Test
In Arizona, a person tested at the State's request has the right to arrange an independent test by a person of their own choosing — at their own expense — and police may not unreasonably interfere with that right. Officers who deny a phone call, refuse access to release for testing, or run out the clock can taint the State's own evidence. The State must also preserve a sufficient blood sample for independent retesting on request.
Implied Consent & the 30-Day MVD Clock
By driving in Arizona you've impliedly consented to chemical testing after a lawful DUI arrest. When an officer serves an admin-per-se or implied-consent suspension order, you have 30 days to request an MVD hearing — miss it, and the suspension takes effect automatically with no hearing at all. The hearing is also your earliest chance to question the officer under oath, months before trial.
Refusal Consequences
Refusing the post-arrest chemical test triggers a 12-month license suspension for a first refusal (24 months for a second within 84 months) — and police can usually get a telephonic warrant and take the blood anyway. Unlike field sobriety tests, which carry no statutory refusal penalty, chemical-test refusal has real, immediate licensing consequences.
From Lab Bench to Courtroom
Every Failure Mode Maps to a Motion
Chemical-test problems are not just talking points — each one corresponds to a specific filing with a specific legal basis. The first step is almost always the same: demand the records. Calibration logs, maintenance histories, blood-kit lot numbers, storage temperature data, chromatograms, and the analyst’s proficiency records.
| Failure Mode | The Filing It Supports |
|---|---|
| Warrantless or coerced blood draw | Motion to suppress (Fourth Amendment — McNeely / Birchfield) |
| Deprivation period not observed | Motion to suppress breath results / foundation challenge |
| Calibration or maintenance lapses | Records request + motion in limine on the number |
| Preservative, storage, or fermentation issues | Expert-supported reliability challenge; retest of preserved sample |
| Chain of custody gaps | Foundation objection + motion to preclude the result |
| Independent-test right denied | Motion to suppress / dismiss for due-process violation |
Get the Records. Then Get to Work.
The Motion Bank’s “More Time” package includes the lab-records requests — calibration logs, maintenance histories, chromatograms, chain-of-custody documents — that start every chemical-test challenge, plus the suppression motions that follow what the records reveal.
Explore the Motion BankBreath & Blood Testing FAQ
Can police take my blood without a warrant in Arizona?
Generally no. A blood draw is a Fourth Amendment search, and under Missouri v. McNeely the natural dissipation of alcohol does not automatically create an exigency excusing the warrant requirement. Police need a warrant, your valid voluntary consent, or genuine case-specific exigent circumstances. Birchfield v. North Dakota confirmed blood draws cannot be justified merely as a search incident to arrest. In practice Arizona officers obtain telephonic warrants quickly — but a draw taken without one, or with consent obtained through misleading advisements, can be challenged.
Is the breath test or the blood test more accurate?
Blood testing by headspace gas chromatography is considered more accurate than breath testing, which is why Arizona agencies predominantly use blood draws. But 'more accurate' is not 'infallible': blood results depend on proper draw technique, adequate preservative in the gray-top tube, refrigerated storage, intact chain of custody, and a lab run with valid controls — and every result carries a stated measurement uncertainty. Breath testing adds the 2100:1 partition-ratio assumption and mouth-alcohol risk on top.
What is the gray-top tube and why does it matter?
Forensic blood samples are collected in gray-stoppered tubes containing sodium fluoride, which prevents microbial activity, and potassium oxalate, which prevents clotting. If the preservative is insufficient, expired, or never mixed into the sample, microbes can ferment the blood's sugars into new alcohol after the draw — inflating the result with alcohol your body never contained. Tube lot numbers, expiration dates, inversion technique, and storage temperatures are all discoverable.
Can I get my own blood test after a DUI arrest in Arizona?
Yes. A.R.S. § 28-1388(C) gives you the right to arrange an independent test by a qualified person of your own choosing, at your own expense, and law enforcement may not unreasonably interfere with that right. Separately, you can demand that the State preserve a portion of its sample so your own lab can retest it. Interference with the independent-test right is itself grounds for a motion.
How long do I have to fight the license suspension?
Thirty days. Under A.R.S. § 28-1385, you have 30 days from service of the suspension order to request an MVD hearing. The request pauses the suspension until the hearing is held. Miss the deadline and the suspension activates automatically — no hearing, no review. This administrative clock runs completely separately from your criminal court dates.
What happens if I refuse the chemical test?
A first refusal brings a 12-month license suspension (24 months for a second refusal within 84 months), and officers can typically obtain a telephonic warrant and draw blood anyway — so a refusal often produces both the suspension and the blood evidence. Note the contrast with field sobriety tests, which you may decline in Arizona with no statutory penalty.