Arizona DUI Blood Test: Can You Challenge the Results?
A blood test can be one of the most important pieces of evidence in an Arizona DUI case. When a laboratory report shows a blood alcohol concentration of .08 or higher, or identifies a drug in someone's system, it may seem as though the scientific evidence makes the case impossible to fight.
That is not necessarily true.
You can challenge DUI blood test results in Arizona. Depending on the circumstances, a defense may involve how police legally obtained the blood, whether the blood draw was performed properly, how the sample was stored and transported, laboratory procedures, chain of custody, the reliability of the analysis, the uncertainty associated with the reported result, or what the concentration actually establishes about the defendant's condition at the time of driving.
Arizona also gives a person tested by law enforcement a reasonable opportunity to arrange for an independent test by a qualified person of the defendant's choosing.
For someone charged with DUI in Phoenix, Mesa, Gilbert, Chandler, Scottsdale, Tempe, or elsewhere in Arizona, a laboratory number should be treated as evidence to investigate, not simply a result that must be accepted automatically.
Quick Answer: Yes. An Arizona DUI blood test can potentially be challenged on both legal and scientific grounds. Depending on the case, an attorney may investigate whether police had a warrant or valid exception to the warrant requirement, whether the sample was properly collected and preserved, whether chain of custody can be established, whether the laboratory followed reliable testing procedures, and whether the reported alcohol or drug concentration actually proves the charged DUI offense.
Why Does Arizona Use Blood Tests in DUI Cases?
Arizona law allows testing of a person's blood, breath, urine, or other bodily substance to determine alcohol concentration or drug content under its implied-consent framework. The test or tests are selected by the law-enforcement agency.
Blood testing is frequently used when police suspect:
Alcohol impairment;
Drug impairment;
A combination of alcohol and drugs;
Prescription-drug impairment;
Marijuana-related DUI;
A serious collision;
Aggravated DUI; or
Other circumstances in which law enforcement seeks chemical evidence.
Unlike a breath test that can generate a result relatively quickly, blood is generally collected and later submitted to a laboratory for analysis.
The resulting report can become important evidence in both alcohol and drug DUI prosecutions.
But the existence of a laboratory result does not eliminate the State's burden of proving the elements of the charged offense beyond a reasonable doubt.
What Does the State Have to Prove in an Arizona DUI Case?
Arizona has several different ways a person can violate its DUI statute.
Under A.R.S. § 28-1381(A), it is unlawful to drive or be in actual physical control of a vehicle:
While impaired to the slightest degree by alcohol, drugs, a qualifying vapor-releasing substance, or a combination;
With an alcohol concentration of .08 or more within two hours of driving or being in actual physical control, when the concentration results from alcohol consumed before or while driving;
While certain drugs defined by Arizona law or their metabolites are in the person's body, subject to statutory defenses;
With an alcohol concentration of .04 or more while operating a commercial motor vehicle requiring a CDL; or
At .04 or more while operating a vehicle for hire or providing transportation-network services as specified by the statute.
This distinction is important.
A blood result does not have exactly the same significance in every DUI prosecution.
For example, in a typical alcohol DUI case, prosecutors may charge both:
A.R.S. § 28-1381(A)(1): impaired to the slightest degree; and
A.R.S. § 28-1381(A)(2): alcohol concentration of .08 or more within two hours of driving.
Those are separate theories of DUI.
Successfully challenging the State's blood-alcohol evidence may therefore affect the charges differently depending on the remaining evidence.
Can You Challenge a DUI Blood Test in Arizona?
Yes.
There are generally two broad areas to investigate:
1. Whether police lawfully obtained the blood, and
2. Whether the blood-test result is scientifically reliable and proves what the prosecution says it proves.
These are different questions.
A laboratory may have performed an analytically sound test on a blood sample that police obtained through an unconstitutional search.
Conversely, police may have lawfully obtained a sample, but legitimate questions may remain about collection, storage, laboratory analysis, interpretation, or the significance of the reported result.
An effective review of a blood DUI case may therefore extend well beyond simply reading the BAC number printed on the laboratory report.
Does Police Need a Warrant to Draw Blood for a DUI in Arizona?
The answer depends on the circumstances.
A blood draw is a search for purposes of the Fourth Amendment. A warrant is one recognized way law enforcement can lawfully obtain a blood sample. Other legally recognized exceptions to the warrant requirement may apply in particular circumstances.
Arizona also has an implied-consent statute, A.R.S. § 28-1321, under which motorists are deemed to have given consent to chemical testing in specified DUI circumstances. But Arizona's implied-consent law does not simply give officers unrestricted authority to conduct every warrantless blood draw.
The Arizona Supreme Court has explained that the statute generally does not authorize law enforcement to administer testing without a warrant unless the driver expressly agrees, subject to other lawful bases for obtaining the sample.
This makes the circumstances surrounding the blood draw important.
An Arizona DUI attorney may investigate:
Was there a search warrant?
What facts were presented to obtain it?
Did the warrant authorize the blood draw that occurred?
If there was no warrant, what exception does the State rely upon?
Did the defendant actually consent?
Was that consent voluntary?
Were statements or conduct improperly used to obtain purported consent?
Was the blood obtained through another statutory procedure?
The answers can affect whether suppression litigation is appropriate.
Does Arizona's Implied Consent Law Mean You Automatically Consent to a Warrantless Blood Draw?
Not quite.
Arizona's implied-consent statute provides that a person operating a motor vehicle in Arizona gives consent to qualifying chemical testing when the statutory requirements are satisfied. After an arrest, however, the statute provides that the person shall be requested to submit to and successfully complete the test.
The Arizona Supreme Court addressed an important distinction in State v. Valenzuela.
There, an officer told a DUI arrestee that Arizona law required him to submit to testing. The Arizona Supreme Court held that the State had not established voluntary consent merely because the defendant agreed after being told he was legally required to submit. The Court explained that consent cannot be established merely through acquiescence to a claim of lawful authority.
That does not mean every blood draw without traditional voluntary consent is automatically suppressed. A warrant or another lawful basis may exist.
It does mean that how police obtained the sample matters.
What Happens If You Refuse a DUI Blood Test in Arizona?
Refusing chemical testing can create consequences separate from the criminal DUI case.
Under A.R.S. § 28-1321, after a DUI arrest a person is requested to submit to testing. The statute provides for a 12-month driver's license suspension or denial for a refusal, and a two-year suspension or denial for a second or subsequent refusal within 84 months, subject to the procedures and requirements contained in the statute.
A refusal also does not necessarily prevent police from obtaining blood.
Depending on the circumstances, law enforcement may seek a search warrant authorizing a blood draw.
Arizona law also makes evidence of a refusal admissible in civil or criminal proceedings, with the fact finder deciding whether the refusal occurred.
Because criminal DUI proceedings and driver's-license proceedings involve different issues and timelines, a person facing a refusal allegation should consider both.
How Is DUI Blood Tested?
The precise laboratory procedure varies, but alcohol testing commonly involves analytical instrumentation designed to determine the concentration of ethanol in a blood sample.
One method frequently encountered in forensic alcohol testing is headspace gas chromatography.
Rather than treating the final laboratory number as self-proving, the defense may obtain and examine underlying laboratory materials.
Depending on the case, those materials can include:
Chromatograms;
Calibration information;
Quality-control results;
Laboratory worksheets;
Instrument-maintenance records;
Batch data;
Internal standards;
Sample records;
Analyst notes;
Laboratory protocols; and
Other information relevant to the particular analysis.
An experienced defense attorney working with an appropriate expert can evaluate whether the laboratory's procedures and underlying data support the reported result.
How Can an Arizona DUI Blood Test Be Challenged?
There is no single defense that applies to every blood test.
Instead, the defense should examine the entire process from collection to courtroom.
1. Challenging the Legality of the Blood Draw
Before debating the laboratory result, the defense can examine whether police lawfully obtained the sample.
Potential issues can involve:
The validity and scope of a search warrant;
Voluntary consent;
Whether an exception to the warrant requirement actually applied;
The circumstances under which consent was requested;
Statements made by officers regarding a person's obligation to provide blood; and
Compliance with applicable constitutional and statutory requirements.
When a constitutional violation is established, the defense may seek suppression of evidence through an appropriate motion.
Whether suppression is available depends on the particular facts and law.
2. Challenging Who Drew the Blood
Arizona law provides that when blood is drawn under A.R.S. § 28-1321, it may be drawn by a physician, registered nurse, or another qualified person.
The statute also contains an important evidentiary provision: the qualifications of the person withdrawing the blood and the method used to withdraw it are not foundational prerequisites to admissibility of a blood-alcohol determination under that subsection.
That distinction matters.
It would be inaccurate to suggest that every deviation during a blood draw automatically makes the BAC result inadmissible. Instead, the significance of a collection problem depends on the nature of the issue and how it affects the legal or scientific reliability of the evidence.
3. Challenging Collection Procedures
Blood evidence begins with the collection itself.
The defense may investigate:
What collection kit was used;
Whether the tubes were appropriate;
How the tubes were labeled;
Whether required components were present;
How the sample was handled immediately after collection;
Whether the tubes were properly sealed; and
Whether documentation matches the actual samples tested.
Not every irregularity invalidates a test.
The important question is whether a particular problem meaningfully affects the reliability, identification, or admissibility of the evidence.
4. Challenging the Chain of Custody
After blood is drawn, it may pass through several hands before analysis.
For example:
blood draw → evidence packaging → law-enforcement storage → transportation → laboratory intake → laboratory storage → analysis
Records should allow the State to establish that the sample tested is connected to the defendant and has been appropriately accounted for.
A defense review may examine:
Evidence labels;
Seals;
Property records;
Transfer logs;
Laboratory accession records;
Storage information; and
Any unexplained discrepancies.
A minor paperwork issue does not necessarily destroy the State's case. But a material break or inconsistency can warrant closer scrutiny.
5. Challenging Storage and Preservation
Blood is biological evidence.
How it is collected and preserved can therefore matter.
The defense may investigate the sample's condition, storage history, preservatives or anticoagulants associated with the collection system, and any circumstances that could affect sample integrity.
The key is not merely identifying that something was "different" from an ideal procedure. The defense must evaluate whether the difference has scientific significance for the particular sample and result.
6. Challenging Laboratory Procedures
A laboratory instrument does not simply produce an unquestionable number.
Reliable forensic testing depends on validated procedures and appropriate quality controls.
A defense expert may examine issues involving:
Calibration;
Controls;
Instrument performance;
Sample preparation;
Analytical separation;
Identification criteria;
Duplicate analyses;
Carryover;
Interferences;
Documentation; and
Compliance with laboratory protocols.
An abnormality does not automatically mean the result is wrong. But the underlying data can sometimes reveal information that is not obvious from the final one-page laboratory report.
7. Challenging Measurement Uncertainty
Scientific measurements are not infinitely precise.
When a reported blood-alcohol concentration is close to a legally significant threshold, the precision and uncertainty associated with the analysis may deserve particular attention.
For example, Arizona's ordinary per se DUI threshold is .08, while Arizona's extreme-DUI statutes use higher alcohol-concentration thresholds (0.15/0.20) that can substantially affect sentencing exposure.
A reported result near a statutory boundary can therefore deserve closer scrutiny than simply treating the reported digits as absolute mathematical certainty.
The specific significance of uncertainty depends on the testing method, laboratory practices, applicable evidentiary rules, and facts of the case.
What If the Blood Was Drawn More Than Two Hours After Driving?
Timing can be extremely important.
Arizona's ordinary per se alcohol DUI statute prohibits having an alcohol concentration of .08 or more within two hours of driving or actual physical control, when the concentration results from alcohol consumed before or while driving.
Sometimes, however, the actual blood draw occurs later.
A laboratory result reflects the concentration in the sample when the blood was drawn, not automatically the person's precise alcohol concentration at an earlier moment.
This can lead to issues involving retrograde extrapolation.
What Is Retrograde Extrapolation?
Retrograde extrapolation is an attempt to estimate a person's earlier blood-alcohol concentration based on a later measurement.
The concept may sound simple—alcohol concentration generally decreases as the body eliminates alcohol—but applying it to a particular person at a particular time can involve assumptions.
Relevant factors may include:
When drinking began;
When drinking ended;
Amount and type of alcohol consumed;
Food consumption;
Whether alcohol was still being absorbed;
Time of driving;
Time of blood draw; and
Assumptions concerning elimination.
For example, a person whose BAC was falling at the time of the blood draw presents a different factual situation from someone who may still have been absorbing alcohol.
When the State relies on an estimate of an earlier BAC, the assumptions underlying that estimate can become an important part of the defense analysis.
Can Your BAC Be Higher at the Time of the Blood Draw Than When You Were Driving?
Yes, potentially.
Alcohol does not enter the bloodstream instantaneously.
After a person consumes alcohol, it is absorbed into the bloodstream over time. Depending on the timing of drinking and other circumstances, a person's alcohol concentration may still be rising after driving has ended.
This is sometimes described as a rising BAC issue.
Suppose a person drinks shortly before leaving a location, drives for a brief period, is stopped, and then has blood drawn considerably later.
A later blood result does not, standing alone, establish that the person's BAC was identical at the earlier time of driving.
The exact significance depends on the evidence and the particular DUI charge.
What If the Blood Test Is Over .08?
A result over .08 is important evidence, but it does not eliminate every potential defense.
Arizona law provides that an alcohol concentration of .08 or more within two hours can give rise to a presumption that the defendant was under the influence, subject to the statutory framework.
More importantly, A.R.S. § 28-1381(A)(2) makes an alcohol concentration of .08 or more within two hours of driving a substantive DUI offense when the statutory requirements are satisfied.
The defense may still investigate:
Whether the blood was lawfully obtained;
Whether the sample belongs to the defendant;
Whether the laboratory result is reliable;
Whether the State can establish the required timing;
Whether alcohol consumed after driving is implicated;
Whether retrograde extrapolation is necessary;
Whether another element of DUI can be proven; and
Whether evidence should be suppressed for an independent legal reason.
A BAC above .08 should therefore be taken seriously, but it should not end the investigation.
What If the Blood Test Shows .15 or .20 or Higher?
Arizona has enhanced DUI offenses based on higher alcohol concentrations.
Under Arizona's extreme-DUI statute, A.R.S. § 28-1382, an alcohol concentration of .15 or more within two hours of driving can trigger an extreme DUI charge, and .20 or more carries still greater mandatory sentencing consequences.
That makes accurate analysis particularly important when a result is near one of these thresholds.
A result just above .15 or .20 can potentially change the offense category and sentencing exposure.
Accordingly, defense counsel may pay close attention to the underlying laboratory data and the timing of the evidence when a result falls near a statutory threshold.
Can You Independently Test the Blood?
Yes, and this can be extremely important.
Arizona law expressly provides that a person tested by law enforcement must be given a reasonable opportunity to arrange for a physician, registered nurse, or other qualified person of the person's own choosing to administer an additional test or tests.
This is commonly called the right to an independent test.
An independent test can potentially provide evidence that can be compared with the government's result.
However, timing matters because alcohol concentration changes over time.
A person arrested for DUI should not assume that the police or prosecutor will automatically arrange an independent test on the defendant's behalf.
What Happens If Police Interfere With Your Ability to Obtain an Independent Test?
The right to attempt to obtain independent evidence can become a significant issue in a DUI defense.
A.R.S. § 28-1388(C) expressly requires that a tested person receive a reasonable opportunity to arrange an additional test by a qualified person of their choosing. The statute also says that a person's failure or inability to obtain that additional test does not, by itself, prevent admission of the government's test.
That statutory language does not mean police are free to improperly interfere with a person's reasonable opportunity to obtain potentially exculpatory evidence.
If an independent test was requested but could not be obtained, a defense attorney should investigate exactly what occurred rather than assuming the issue is irrelevant.
Can Hospital Blood Be Used in an Arizona DUI Case?
Potentially.
Arizona law contains a provision addressing blood, urine, or another bodily substance obtained for another reason.
Under A.R.S. § 28-1388(E), if an officer has probable cause to believe a person violated A.R.S. § 28-1381 and a sample of blood, urine, or another bodily substance is taken from that person for any reason, a sufficient portion must be provided to law enforcement if requested for law-enforcement purposes.
Hospital-blood cases can raise issues different from a standard police blood kit.
Depending on the circumstances, those issues can involve how law enforcement obtained the sample or information, what type of testing the hospital performed, and how the evidence relates to the criminal allegations.
What About Drug DUI Blood Tests?
Blood testing is not limited to alcohol.
Arizona DUI prosecutions can involve:
Marijuana;
Prescription medications;
Fentanyl and other opioids;
Methamphetamine;
Cocaine;
Benzodiazepines;
Sleep medications; and
Other drugs.
The legal analysis can be substantially different from an alcohol DUI.
Under A.R.S. § 28-1381(A)(1), prosecutors can allege that a drug impaired the person to the slightest degree.
A.R.S. § 28-1381(A)(3) separately addresses driving while a drug defined in A.R.S. § 13-3401 or its metabolite is in the person's body, subject to statutory limitations and defenses. Arizona specifically provides a defense to an (A)(3) prosecution for a person using a drug as prescribed by an authorized medical practitioner.
Finding a drug in someone's blood does not necessarily answer every question about impairment.
Depending on the substance, concentration, timing, metabolites, prescription status, and charge, toxicological interpretation may become important.
Can a DUI Blood Test Be Thrown Out?
Potentially.
"Throwing out the blood test" can refer to several different things.
A court might suppress blood evidence because of a constitutional violation. In another case, a particular evidentiary problem might affect admissibility. In still another, the result may be admitted but attacked before the jury through cross-examination or expert testimony.
Those outcomes are legally different.
It is therefore better to ask:
What weakness exists in this particular blood test, and what legal remedy follows from that weakness?
Not every laboratory mistake results in suppression. Not every chain-of-custody dispute results in exclusion. And not every constitutional issue ultimately eliminates the evidence.
But those issues can materially affect a DUI prosecution and should be investigated when the facts support them.
Does Challenging the Blood Test Automatically Dismiss the DUI?
No.
Even if blood evidence is suppressed or substantially weakened, prosecutors may have other evidence.
That could include:
Driving behavior;
An accident;
Body-camera footage;
Field sobriety tests;
Admissions about drinking;
Open containers;
Witness testimony;
Physical observations;
Drug evidence; or
Other circumstantial evidence.
This is particularly relevant to an A.R.S. § 28-1381(A)(1) charge alleging impairment to the slightest degree.
The effect of successfully challenging blood evidence therefore depends on what charges were filed and what other admissible evidence remains.
What Should an Arizona DUI Attorney Review in a Blood-Test Case?
A meaningful DUI blood defense should go beyond looking at the final BAC number.
Depending on the case, counsel may want to obtain and evaluate:
Police reports;
Body-camera footage;
Search warrant and affidavit;
Blood-draw records;
Blood-kit documentation;
Evidence logs;
Chain-of-custody records;
Laboratory report;
Chromatograms and underlying analytical data;
Calibration and quality-control records;
Instrument records;
Analyst documentation;
Hospital records when applicable;
Dispatch and timing records;
Drinking history relevant to BAC timing;
Independent-test evidence; and
Relevant MVD documents.
Some cases may also warrant consultation with a forensic toxicologist or other qualified expert.
The goal is not to invent a scientific challenge where none exists. It is to determine whether the government's evidence withstands careful legal and scientific review.
Frequently Asked Questions About Arizona DUI Blood Tests
Can you fight a DUI if the blood test is over .08?
Yes. A result over .08 is significant evidence, but potential issues can still involve the legality of the blood draw, laboratory reliability, chain of custody, timing, rising BAC, retrograde extrapolation, and other elements of the charged offense.
Can police take your blood without your consent in Arizona?
Police may obtain blood pursuant to a valid search warrant or another legally recognized basis. Arizona's implied-consent statute does not mean that every warrantless, nonconsensual blood draw is automatically lawful. The particular circumstances must be examined.
What happens if you refuse a blood test?
A refusal can trigger administrative driver's-license consequences. Under the current Arizona implied-consent statute, a qualifying first refusal carries a 12-month suspension or denial, while a second or subsequent refusal within 84 months can result in two years. Police may also seek a warrant for blood, and evidence of refusal may be admissible.
How long after driving can police draw blood?
There is not a simple rule that makes a blood draw automatically invalid merely because a particular amount of time has passed. But timing can be critical because Arizona's ordinary per se DUI offense concerns an alcohol concentration of .08 or more within two hours of driving or actual physical control. A later blood draw may require additional evidence concerning the earlier concentration.
Can a DUI blood sample be independently tested?
Arizona law gives a tested person a reasonable opportunity to arrange for an additional test by a qualified person of the person's choosing.
Can a laboratory make a mistake?
Laboratory testing is performed under scientific procedures and quality-control systems, but laboratory evidence is still evidence that can be examined. Depending on the case, the defense may review calibration, controls, chromatograms, documentation, instrument performance, sample handling, and other underlying data.
What if my BAC was still rising?
If alcohol was still being absorbed, a later blood result could potentially be higher than the person's concentration at an earlier time. Whether a rising-BAC issue helps the defense depends on drinking history, timing, the laboratory result, the charge, and other evidence.
Can prescription medication cause a DUI?
Yes. Arizona can prosecute driving while impaired to the slightest degree by a drug even when the drug was lawfully prescribed. However, Arizona also provides a statutory defense to the separate A.R.S. § 28-1381(A)(3) drug-or-metabolite offense when the drug was used as prescribed by an authorized medical practitioner.
Charged With a Blood-Test DUI in Phoenix or the East Valley?
A DUI blood result can be powerful evidence, but a laboratory number should not be confused with an automatic conviction.
The legality of the blood draw, timing of the sample, chain of custody, laboratory procedures, underlying analytical data, alcohol absorption and elimination, independent testing, and the elements of the particular DUI charge can all matter.
At Millar Law, we represent clients facing DUI and criminal charges throughout the Phoenix metropolitan area, including Gilbert, Mesa, Chandler, Scottsdale, Tempe, Phoenix, and throughout Arizona.
Contact us today if you or a loved one is charged with DUI in Arizona to learn about how we can help at 602-900-0545.
If your DUI case involves a blood draw, an experienced Arizona DUI defense attorney can review both the legal basis for obtaining the sample and the scientific evidence underlying the reported result.
This article is general information about Arizona law and is not legal advice. DUI cases are fact-specific, and the availability of any particular challenge or defense depends on the evidence and circumstances.
