Blood and Breath Test Challenges in Wisconsin
Arrested for an OWI? A test result isn’t the end of your case. Call or schedule a free consultation with Chirafisi Anderson, S.C. today.
Understanding Chemical Testing in Wisconsin OWI Cases
After an OWI arrest in Wisconsin, law enforcement typically requires a chemical test—most commonly a breath or blood test—to measure alcohol concentration or detect restricted controlled substances such as THC, cocaine, or methamphetamine.
These test results often become the central evidence in an OWI prosecution. However, chemical testing is governed by strict statutory, administrative, and scientific requirements. Errors in equipment calibration, operator certification, sample handling, or testing procedures can lead to false, exaggerated, or legally unreliable results.
At Chirafisi Anderson, S.C., we treat chemical test results as evidence to be challenged—not accepted at face value. Our attorneys regularly defend clients throughout Southern and Central Wisconsin, including Dane, Rock, Jefferson, Columbia, Sauk, Iowa, Dodge, and Green Counties, by scrutinizing whether breath, blood, or urine testing complied with Wisconsin law and constitutional standards.
Chemical test challenges frequently determine whether an OWI case survives pretrial litigation, particularly when prohibited alcohol concentration (PAC) or drug-test results form the basis of the State’s case.
Legal Standards for Chemical Tests in Wisconsin
Chemical testing in Wisconsin OWI cases is governed by the state’s implied consent law, which allows law enforcement to request a breath, blood, or urine test when there is probable cause to believe a person operated while under the influence. However, the State bears the burden of proving that the test was obtained and analyzed in strict compliance with Wisconsin law and administrative regulations.
Under Wisconsin law, the State must establish each of the following:
- The test was lawfully requested under Wisconsin’s implied consent law.
Officers must have had probable cause to arrest and must comply with the statutory requirements of Wis. Stat. § 343.305 before requesting a chemical test. Failures at this stage can support suppression of the test result or dismissal of related refusal allegations. - The test was administered using approved methods.
Breath, blood, and urine tests must be conducted in accordance with Wisconsin Department of Transportation–approved procedures. Deviations from required methods undermine the reliability and admissibility of the results. - The operator or analyst was properly certified.
Breath-test operators and laboratory analysts must hold valid certifications at the time of testing. Expired or missing certifications can render results unreliable. - The equipment was properly maintained and calibrated.
Breath-testing instruments and laboratory equipment must be maintained and calibrated according to regulatory schedules. Missing logs, overdue maintenance, or undocumented repairs are common grounds for challenge.
If the State cannot prove each of these requirements, the chemical test result may be suppressed, excluded, or given little evidentiary weight at trial. In many OWI cases—particularly those based on prohibited alcohol concentration (PAC) or restricted controlled substances —chemical test compliance is the central issue that determines whether the prosecution can proceed.
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Types of Chemical Tests Used in Wisconsin
Wisconsin law permits three primary types of chemical tests in OWI investigations: breath, blood, and urine. Each test type is governed by different scientific standards and presents distinct opportunities for legal challenge.
Breath Tests
Breath testing is the most common method used after an OWI arrest and is typically administered at a law enforcement facility using an evidentiary breath-testing instrument approved by the Wisconsin Department of Transportation.
Wisconsin currently uses instruments such as the Intoximeter EC/IR II, which rely on infrared spectroscopy to estimate alcohol concentration. Breath test results are highly sensitive to procedural compliance and are vulnerable to challenge when:
- The device was not properly calibrated or maintained
- The operator lacked valid certification
- Required observation periods were not followed
- Environmental or physiological factors affected the sample
Common physiological factors—such as acid reflux, GERD, recent dental work, or residual mouth alcohol—can artificially inflate breath results. Because breath testing estimates alcohol in the breath rather than directly measuring blood alcohol, even small deviations can materially affect results used to allege a prohibited alcohol concentration (PAC).
Blood Tests
Blood testing is increasingly common in Wisconsin, particularly in cases involving refusals, accidents, or suspected drug impairment. Blood draws must be conducted by a qualified medical professional and handled in compliance with statutory and laboratory standards.
Blood test challenges frequently focus on:
- Improper collection techniques
- Labeling or documentation errors
- Failures in refrigeration or storage
- Breaks in chain of custody
- Laboratory contamination or fermentation
Unlike breath tests, blood analysis often requires expert testimony to explain how post-collection issues can alter reported alcohol or drug concentrations. Blood testing is also commonly used to detect restricted controlled substances, including THC, cocaine, and methamphetamine, which raises additional scientific and legal issues related to impairment versus mere presence.
Urine Tests
Urine testing is rarely used in Wisconsin OWI cases and is primarily employed to detect the presence of drugs or restricted controlled substances. Courts generally treat urine results with caution because urine testing does not measure impairment at the time of driving.
Key limitations of urine testing include:
- Urine tests detect metabolites, not active impairment
- Results do not establish when a substance was consumed
- Delayed testing can produce misleading positives
- Cross-contamination risks are higher than with blood or breath samples
Because urine testing is non-quantitative, it is typically insufficient on its own to prove impairment and is most often challenged on relevance and reliability grounds.
Preliminary Breath Tests (PBTs) in Wisconsin
Before making an OWI arrest, officers often request a Preliminary Breath Test (PBT) using a handheld device at the roadside. A PBT is a screening tool, not an evidentiary chemical test.
Under Wis. Stat. § 343.303, an officer may request a PBT only after developing probable cause to believe a person is operating while under the influence. The role of the PBT is limited to helping an officer decide whether to arrest—not to prove guilt.
Key points about PBTs in Wisconsin:
- You are not required to take a PBT. Refusing a PBT is not a violation of Wisconsin’s implied consent law and does not trigger license penalties, however, your refusal can be used as probable cause for arrest.
- PBT results are not admissible to prove guilt at trial. They may be used only to assess probable cause or to support pretrial motions.
- PBT devices are less accurate than evidentiary breath tests. Roadside conditions, temperature changes, device variability, and limited calibration controls make PBT results particularly vulnerable to error.
Because PBTs are often relied upon to justify an arrest, errors or inconsistencies in PBT administration can be critical. Our attorneys frequently use PBT issues to challenge whether probable cause existed for the arrest in the first place, which can result in suppression of all evidence obtained afterward—including breath or blood test results.
How We Challenge Chemical Test Evidence
At Chirafisi Anderson, S.C., we approach chemical test results as evidence to be tested—not accepted. Chemical test challenges often begin before formal charges are filed and can determine whether the State’s case survives pretrial litigation, particularly when BAC or drug results are the prosecution’s primary evidence.
Our process focuses on identifying statutory, administrative, and scientific failures that undermine reliability and admissibility, including:
When these issues are established, courts may suppress test results, exclude them from evidence, or significantly limit their weight—often changing the trajectory of the case.
For a broader explanation of how chemical-test challenges fit into pretrial litigation and suppression practice, see our OWI dismissal and defense strategies page.
Chemical Test Lawyers in Wisconsin
Challenging chemical test evidence requires more than familiarity with OWI law—it requires experience litigating technical evidentiary issues and understanding how Wisconsin courts actually evaluate breath, blood, and drug-testing challenges.
At Chirafisi Anderson, S.C., our attorneys routinely litigate chemical test issues in both misdemeanor and felony OWI cases throughout Southern and Central Wisconsin, including Dane, Rock, Jefferson, Columbia, Sauk, Iowa, Dodge, and Green Counties. We understand how local courts scrutinize breath-test reliability, blood-draw warrants, laboratory procedures, and expert testimony.
Importantly, chemical test challenges are often case-dispositive. Successful suppression or exclusion of test results can fundamentally alter the State’s ability to proceed—particularly in cases where numerical results are the primary evidence of impairment.
Our approach focuses on identifying the issues that matter in practice, preserving suppression arguments early, and positioning cases for dismissal, reduction, or favorable resolution when chemical evidence cannot withstand scrutiny.
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A chemical test result does not determine the outcome of your OWI case. Breath, blood, and drug-test evidence must meet strict legal and scientific standards, and failures at any stage can significantly weaken—or eliminate—the State’s case.
If you were arrested for OWI and chemical testing is central to the prosecution, contact Chirafisi Anderson, S.C. for a free consultation. We represent clients throughout Southern and Central Wisconsin, including Dane, Rock, Jefferson, Dodge, Columbia, Sauk, Iowa, and Green Counties, and focus on identifying test-related issues early—before they become locked into the case.