Preliminary Breath Test (PBT) vs. Post-Arrest Breath/Blood Test
In a Michigan OWI stop, the roadside PBT and the post-arrest evidentiary test serve entirely different legal purposes. The PBT is primarily used to help establish probable cause for an arrest and has only limited admissibility as direct evidence of intoxication at trial. The post-arrest evidentiary test is the one that can follow you into court.
What is the difference between the breath test the officer gave you on the side of the road and the one they want you to take at the police station? They are not the same test, and Michigan law does not treat them the same way. The roadside test, called a preliminary breath test or PBT, helps an officer decide whether to place you under arrest. The test after your arrest, whether breath or blood, is the one that can be admitted as evidence at trial. A Michigan OWI attorney can walk you through what each result means for your case and what you should do next.
What Is a Preliminary Breath Test in Michigan?
A preliminary breath test, or PBT, is a roadside screening tool. During a traffic stop, before any arrest has been made, an officer can use a small handheld device to get a quick reading of your breath alcohol content (BAC) if they have reason to suspect you have been drinking. The test takes seconds, and the result is available immediately at the scene.
Under Michigan’s preliminary breath test statute, the PBT can be used by an officer to decide whether to make an arrest, and the result can be considered in challenges to the validity of an arrest. However, PBT results are not introduced as direct evidence of intoxication in an OWI prosecution. The handheld device is treated as a screening tool rather than the evidentiary instrument used to prove blood alcohol content if there is a trial.
Refusing a PBT in Michigan is a civil infraction for non-commercial drivers. There is no license suspension and no points added to your driving record for refusing the roadside test. The Michigan State Police rights advisory read at the roadside informs drivers that refusal carries a fine, and local court fine schedules generally place that fine at a modest amount.
A PBT refusal while operating a commercial vehicle is a misdemeanor under MCL 257.625a. It can trigger immediate out-of-service orders and CDL-specific disqualification consequences that are separate from and in addition to the criminal charge. Commercial drivers should never assume the same rules apply.
That said, a PBT refusal does not end the investigation or prevent an arrest. Officers can still act on other observations, including your driving behavior, the odor of alcohol, slurred speech, and the results of standardized field sobriety tests. Declining the PBT removes one piece of the officer’s probable cause picture, but it does not remove all of them.
What Happens After Arrest: The Evidentiary Breath or Blood Test
Once you are placed under arrest for suspected OWI, a different set of rules applies.
After a lawful OWI arrest, Michigan’s implied consent law means you will be asked to take a chemical test, which is often a breath test administered at the police station, but it can also be a blood test taken by a medical person. Under MCL 257.625, a blood alcohol content of 0.08 percent or higher supports a charge of operating while intoxicated.
This is the test that matters in court. The Intoxilyzer 9000 result is admissible as evidence in an OWI prosecution and can directly support a conviction. A reading of 0.17 percent or above brings the case under Michigan’s High BAC law, sometimes called the Super Drunk law, which carries significantly enhanced criminal penalties.
The device is subject to strict maintenance and calibration requirements. Michigan requires the Intoxilyzer 9000 to be inspected and verified for accuracy at regular intervals. Tests must be administered by a certified operator following specific protocols, including a fifteen-minute observation period before the test to rule out residual mouth alcohol. When those standards are not met, the test result may be open to challenge.
Blood tests must also meet certain requirements, and any failure to do that can give rise to an evidentiary challenge.
Refusing the Post-Arrest Test: What Michigan’s Implied Consent Law Actually Says
Declining the post-arrest evidentiary test has consequences that go well beyond those attached to refusing the roadside PBT. The civil penalties — a one-year license suspension and six points on your driving record for a first refusal — are separate from any criminal OWI charge, which means they can take effect even if the underlying OWI case is later dismissed or results in an acquittal. For a detailed look at how Michigan’s implied consent framework works and what to do if you have already refused, see our articles on breath test refusal and implied consent in Michigan.
How the PBT vs. Evidentiary Test Distinction Shapes Your Defense
Understanding the difference between these two tests matters because it determines where an experienced OWI attorney will focus. If the PBT result was used as the basis for an arrest that was not otherwise supported, an attorney may be able to challenge the legality of the arrest itself. That challenge does not depend on whether the PBT was admissible at trial. It depends on whether the stop and the arrest were constitutionally sound.
On the evidentiary test side, the Intoxilyzer 9000 result comes with its own set of challengeable elements. The breath testing machine must be properly calibrated and maintained, the operator must be certified, and specific protocols must be followed, including the observation period before the test is administered to rule out residual mouth alcohol. Maintenance logs, calibration records are all areas a thorough defense attorney will examine.
If there was a blood test instead of a breath test, the same level of scrutiny must be applied. The blood draw procedure itself and the chain of custody for the sample are areas a thorough defense attorney will carefully examine.
For drivers facing OWI or DUI charges in Wayne, Oakland, Macomb, or one of the surrounding counties, the impact of these tests extends well beyond the criminal case. A conviction can mean license sanctions, elevated insurance rates, and lasting consequences for employment. Our firm brings more than 30 years of concentrated experience in Michigan OWI defense — and a detailed, working knowledge of how these testing procedures operate and where they can be challenged in court.
Facing OWI Charges in Michigan? Our Office Can Help.
If you are trying to figure out what a Michigan OWI arrest means for your future, we’re here to help. Our firm offers free, confidential phone consultations for people facing OWI charges throughout Metro Detroit and across Michigan. Call us Monday through Friday, 8:30 AM to 5:00 PM, at 586-465-1980.
 An after-hours answering service is also available. In addition, you can reach us through the contact form or chat box on our website. For more on how we approach Michigan OWI cases, visit our Michigan DUI defense page.
