Blood tests are treated as the “gold standard” in Michigan OWI cases, but the truth is simple: blood tests are not perfect, not automatic, and not unbeatable. They are performed by human beings, using machines that malfunction, in labs that make mistakes. And when the police or the lab fail to follow the rules, the entire test can be thrown out.
Most people charged with OWI believe that a blood test is the end of the case. It isn’t. A blood test is just evidence — and evidence can be challenged, suppressed, or proven unreliable.
This page explains how blood draws work in Michigan, what the police must do, and how an aggressive OWI attorney can attack the results.
How Blood Draws Work in Michigan OWI Cases
When an officer believes you are under the influence, they can request a chemical test. If they choose a blood test, Michigan law requires strict procedures:
• The officer must have probable cause
• The officer must read the chemical test rights
• The blood must be drawn by a qualified medical professional
• The sample must be collected in a properly sealed, sterile vial
• The vial must contain the correct preservatives and anticoagulants
• The sample must be labeled, sealed, and logged
• The sample must be transported and stored according to protocol
• The lab must follow scientific standards during testing
If any step is done incorrectly, the BAC number becomes unreliable — and unreliable evidence can be challenged.
Common Problems With OWI Blood Tests
Blood tests fail more often than people think. Some of the most common issues include:
• Contamination from improper cleaning or handling
• Fermentation inside the vial, which raises BAC levels
• Expired or incorrect preservatives
• Improper sealing or labeling
• Broken chain of custody
• Unqualified personnel drawing the blood
• Improper storage temperatures
• Lab technician errors
• Machine calibration problems
• Sample mix‑ups
• Delays in testing
Any one of these can create reasonable doubt. Several of them together can destroy the prosecution’s case.
Chain of Custody – The Weak Link in Most Blood Cases
Chain of custody is the paper trail showing who handled your blood sample from the moment it was drawn until the moment it was tested. If the State cannot prove:
• who had the sample
• where it was stored
• how it was transported
• whether it was sealed
• whether it was tampered with
…then the blood test can be suppressed or excluded.
A broken chain of custody is one of the strongest defenses in a Michigan OWI blood case.
How Labs Test Blood – And Where They Go Wrong
Michigan labs typically use headspace gas chromatography to test blood alcohol levels. It’s a reliable method when done correctly — but it depends on:
• proper calibration
• clean equipment
• correct sample preparation
• accurate data entry
• trained technicians
Labs are busy. Technicians are human. Mistakes happen.
Common lab errors include:
• mislabeling samples
• using contaminated equipment
• incorrect calibration
• transcription errors
• failing to run proper controls
• mixing up vials
• reporting the wrong result
These errors can raise BAC levels or produce completely false readings.
Medical Blood Tests vs. Legal Blood Tests
If your blood was drawn at a hospital, the results are often not reliable for legal purposes. Hospitals test blood for medical treatment, not for courtroom accuracy. They use different equipment, different preservatives, and different procedures.
A hospital blood test can be challenged because:
• it is not designed to measure legal BAC
• it may use serum, not whole blood
• serum results can be 15–25% higher
• chain of custody is usually nonexistent
A skilled OWI attorney can often exclude or undermine hospital blood results.
How to Challenge a Blood Test in Court
There are several ways to attack a blood test in a Michigan OWI case. The most effective strategies include:
• Motion to suppress the blood draw (illegal arrest, improper consent)
• Motion to suppress the test results (chain of custody issues)
• Motion to exclude based on lab errors or contamination
• Independent blood testing by a defense expert
• Cross‑examining the officer on procedure
• Cross‑examining the lab technician on scientific errors
• Challenging the margin of error
• Raising reasonable doubt about the accuracy of the number
A blood test is only as strong as the weakest step in the process — and there are many steps.
Why Blood Test Cases Are Winnable
Blood tests look intimidating, but they are vulnerable. I have seen:
• blood samples tested that were not the defendant’s
• vials missing preservatives
• samples stored in hot police cars
• nurses who didn’t know the legal requirements
• officers who skipped steps
• lab techs who admitted mistakes
• BAC numbers that were scientifically impossible
When you know where to look, you find problems.
And when you find problems, you create reasonable doubt.
If You’re Facing a Blood Test OWI in Michigan
Do not assume the case is over. Do not plead guilty because the number looks high. Do not let the State bully you into giving up your rights.
A blood test is evidence — and evidence can be challenged.
Call 248-882-0838
