Criminal Defense Attorney Kevin Kennedy prosecuted DUI cases as a prosecutor in the Davidson County District Attorney’s Office. He now uses that experience to defend clients accused of DUI based on an alcohol concentration of 0.08% or more. Kevin holds his law degree from Vanderbilt Law School and is an active member of the Tennessee Association of Criminal Defense Lawyers.
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A DUI per se charge is built around a number. In Tennessee, the State may allege that a driver violated Tenn. Code Ann. § 55-10-401 because the person’s blood or breath alcohol concentration was 0.08% or more while driving or in physical control of a motor vehicle in a covered location. That number can look decisive, but it is only one part of the prosecution’s case.
A per se DUI defense should examine how the stop began, whether the test was lawfully obtained, whether the instrument or laboratory produced a reliable result, when the sample was taken, and whether the evidence proves the statutory elements beyond a reasonable doubt. The firm’s main Nashville DUI defense page remains the broad guide to DUI charges; this page focuses specifically on the alcohol-concentration theory.
What Is DUI Per Se Under Tennessee Law?
Tennessee’s DUI statute contains more than one way for the State to prosecute a case. Under § 55-10-401(a)(2), a person may be charged when the alcohol concentration in the person’s blood or breath is 0.08% or more. The statute also requires proof that the person drove or was in physical control of a motor vehicle on a public road, highway, parking area, or another location generally frequented by the public.
The phrase “per se” means the State can rely on the prohibited alcohol concentration itself rather than proving every aspect of impairment-based DUI in the same way. It does not mean the case is automatic, and it does not eliminate the other elements of the charge.
DUI Per Se vs. Impairment-Based DUI
An impairment-based DUI focuses on whether alcohol, marijuana, a controlled substance, prescription medication, another drug, or a combination of substances impaired the driver’s ability to operate safely. The State may use driving behavior, body-camera video, officer observations, field sobriety tests, statements, and witness testimony.
A per se case focuses on the chemical-test number. A person with a 0.08% or higher result may face the per se theory even if the driving appeared normal. A person below 0.08% may still face an impairment theory if the State claims the person’s ability to drive safely was affected. Many cases involve both theories, and the defense should separate them rather than treating every DUI as the same case.
The 0.08% BAC Threshold
For many adult non-commercial drivers, 0.08% is the ordinary per se threshold. The result must be tied to the time of driving or physical control. A test taken later at jail, a hospital, or another location may require additional evidence about timing, absorption, elimination, and the person’s drinking history.
Different rules can apply to commercial drivers and underage drivers. A commercial motor vehicle case can involve a 0.04% standard, while underage driving-while-impaired cases involve separate provisions. Learn more about DUI cases involving a CDL and the firm’s broader DUI resources.
Breath Testing in a DUI Per Se Case
Breath testing depends on more than the final printout. The defense should review the instrument, operator, observation period, test sequence, maintenance, calibration, certification, and any error messages or irregularities. Medical conditions, mouth alcohol, recent belching or vomiting, dental work, and other interfering factors may matter depending on the evidence.
The officer’s body-camera footage should be compared with the written report. Video may show whether the required observation period occurred, whether instructions were given correctly, and whether the driver’s statements or physical condition were accurately described.
Blood Testing and Laboratory Evidence
Blood evidence can be powerful, but it requires a lawful draw and reliable scientific handling. The defense should examine whether police relied on consent, a warrant, or another lawful basis; who drew the sample; what kit and preservatives were used; how the sample was sealed, stored, transported, and tested; and whether the laboratory followed its procedures.
Hospital blood and forensic blood are not always interchangeable. A hospital may test serum or plasma for treatment purposes, while a forensic laboratory may test whole blood using a different method. The defense should determine exactly what was tested before accepting the reported number. For a deeper discussion, see the firm’s page on DUI blood-test cases.
Testing Timing and Retrograde Extrapolation
Alcohol does not enter or leave the bloodstream instantly. If a person drank shortly before driving, the alcohol concentration may still have been rising when the vehicle stopped. If substantial time passed before testing, the State may attempt to estimate the earlier concentration through retrograde extrapolation.
That estimate depends on assumptions about the drinking timeline, food, body characteristics, absorption, elimination, and the test time. Incomplete or unreliable assumptions can make the estimate vulnerable. A later result should not automatically be treated as the exact BAC at the time of driving.
Admissibility and Constitutional Issues
A chemical result is not useful to the prosecution unless the State can lawfully obtain and admit it. The defense may challenge the initial stop, the length of the detention, the basis for arrest, the request for testing, consent, the warrant, the blood draw, or the laboratory evidence.
When evidence was obtained through an unconstitutional search or seizure, suppression may be available. A successful challenge can fundamentally change a per se DUI prosecution because the State may lose the numerical evidence at the center of its case.
Penalties in a DUI Per Se Case
DUI per se does not carry a separate sentencing structure. A conviction is sentenced under Tennessee’s ordinary DUI penalty provisions. The potential outcome depends on the offense date, prior qualifying convictions, alcohol concentration, whether a child was in the vehicle, whether an accident or injury occurred, license consequences, and other statutory facts.
A first DUI can involve mandatory jail time, fines, license revocation, alcohol education or treatment, probation, and ignition-interlock issues. Higher alcohol concentrations and prior convictions can increase the required punishment. Because penalty statutes change, the exact exposure should be calculated from the law in effect on the offense date.
Potential Defenses to DUI Per Se Charges
- The traffic stop or detention was unlawful.
- The State cannot prove driving or physical control.
- The location does not satisfy the statute.
- The breath instrument or operator procedure was unreliable.
- The blood draw lacked valid consent, a warrant, or another lawful basis.
- The sample was contaminated, mislabeled, improperly stored, or inadequately documented.
- The laboratory method or analyst records do not support the reported result.
- The test occurred too late to establish the BAC while driving.
- A medical condition or interfering substance affected the result.
- Video or witness evidence contradicts the officer’s account.
Evidence Kevin Kennedy Reviews in a Per Se DUI Case
A complete defense file may include body-camera and dash-camera footage, 911 and dispatch records, the stop timeline, field sobriety videos, breath-test tickets, instrument maintenance and calibration records, operator information, blood-draw records, warrants, hospital records, laboratory reports, chromatograms, quality-control records, chain-of-custody documents, and witness statements.
Kevin’s former-prosecutor experience helps him evaluate how the State will use the BAC number and where the proof may be vulnerable. Depending on the evidence, the defense may challenge the stop, suppress the test, dispute the result, contest driving or physical control, negotiate for a reduction, or prepare the case for trial.
Related Nashville DUI Defense Pages
- Nashville DUI Lawyer
- Nashville First Offense DUI Lawyer
- Nashville DUI With Blood Test Lawyer
- Nashville DUI With CDL Lawyer
- Nashville DUI With Refusal Lawyer
- Nashville Implied Consent Violation Lawyer
Frequently Asked Questions About DUI Per Se
What does DUI per se mean in Tennessee?
DUI per se is the alcohol-concentration theory under Tenn. Code Ann. § 55-10-401. For many adult drivers, the State may proceed on evidence that the person's blood or breath alcohol concentration was 0.08% or more while driving or in physical control of a motor vehicle in a covered location.
Is DUI per se different from impairment-based DUI?
Yes. A per se case focuses on the alcohol concentration, while an impairment case focuses on whether a substance deprived the driver of the clearness of mind and self-control necessary to operate safely. The State may plead or present evidence under both theories.
Can I be convicted below 0.08%?
Potentially. A result below 0.08% does not automatically defeat an impairment-based DUI. The State may rely on driving, officer observations, field sobriety tests, statements, video, and other evidence.
Does a result over 0.08% guarantee a conviction?
No. The State still must prove the required driving or physical-control element, the covered location, a legally obtained and admissible test, and a reliable connection between the reported result and the time of driving.
Are breath tests always accurate?
No test should be treated as infallible. Breath results can be challenged through the instrument's certification, maintenance, calibration, observation period, operator procedure, interfering substances, medical conditions, and documentation.
Can a blood test be challenged?
Yes. A blood case can involve the legal basis for the draw, warrant or consent issues, collection technique, preservatives, storage, chain of custody, laboratory method, analyst records, and the difference between hospital and forensic testing.
Why does testing time matter?
Alcohol concentration can change after driving stops. A later test may not equal the concentration at the time of driving, especially when alcohol was still being absorbed. Retrograde extrapolation depends on assumptions that should be examined.
Can police take blood if I refuse?
Refusal does not necessarily prevent police from seeking a warrant or relying on another lawful basis for a blood draw. The refusal issue and the admissibility of the blood evidence are separate questions.
Does DUI per se have separate penalties?
No. DUI per se is a theory under the general Tennessee DUI statute, not a separate sentencing scheme. Penalties depend on the DUI conviction, prior record, alcohol concentration, child passengers, injuries, and other statutory factors.
What should I do after a per se DUI arrest?
Preserve the citation, bond paperwork, receipts, witness information, and your recollection of the drinking and driving timeline. Ask counsel to obtain body camera, dash camera, breath-instrument records, blood records, laboratory data, and any warrant materials promptly.
Legal references: Tenn. Code Ann. §§ 55-10-401, 55-10-402, 55-10-406, and 55-10-408. This page is general information, not legal advice. DUI law and penalty provisions can change, and the law in effect on the offense date controls.
If you are facing a DUI per se charge in Nashville or Middle Tennessee, call or text Kevin Kennedy Law Firm at (615) 205-7311 for a free, confidential consultation.