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Blood Testing vs. Breath Testing in Michigan OWI Cases
The Short Answer
In Michigan OWI cases, prosecutors typically rely on either breath testing or blood testing to prove alcohol concentration. While both are presented as objective scientific evidence, they work in very different ways and raise very different reliability issues.
Neither test is automatically accurate. The strength of the evidence depends on how the test was conducted, what assumptions were relied upon, and whether the underlying science supports the result.
Understanding the difference between breath and blood testing is essential to evaluating the strength of a DUI case.
Why Michigan Uses Two Different Chemical Tests
Michigan law permits alcohol concentration to be measured using breath or blood testing. The method used usually depends on the circumstances of the case.
Breath testing is most common in routine traffic stops.
Blood testing is more common in crash cases, hospital settings, warrant cases, or situations involving injury or suspected drug use.
Although both methods are often described as “scientific,” they measure alcohol in fundamentally different ways.
How Breath Testing Works in Michigan DUI Cases
Breath testing estimates blood alcohol concentration by measuring alcohol in exhaled breath and applying a mathematical conversion.
This process relies on assumptions about:
- breath-to-blood partition ratios
- body temperature
- breathing patterns
- instrument stability
- controlled testing conditions
In Michigan, most breath tests are conducted using the Intoxilyzer 9000.
Breath testing cases often turn on issues such as:
- machine error and exception rates
- forced or prolonged blowing
- radio-frequency interference
- mouth alcohol from reflux or dental issues
- whether internal diagnostic data reveals instability
A detailed discussion of these issues appears here:
Breath Testing in Michigan DUI Cases
For a deeper look at Michigan’s current breath-testing instrument, see:
Is the Intoxilyzer 9000 Accurate?
How Blood Testing Works in Michigan DUI Cases
Blood testing attempts to measure alcohol concentration more directly, but the process is more complex than many people realize.
In Michigan, blood samples are typically analyzed using headspace gas chromatography with flame ionization detection (GC-FID). The test does not analyze liquid blood itself—it analyzes the vapor above a heated blood sample.
Blood testing cases often turn on issues such as:
- sample preservation and storage
- post-draw fermentation
- use of hospital serum or plasma values
- measurement uncertainty near legal thresholds
- laboratory batch and calibration issues
A full discussion of these issues appears here:
DUI Blood Testing in Michigan OWI Cases
Which Test Is “Better” Evidence?
Neither breath testing nor blood testing is inherently stronger.
Breath testing is immediate and non-invasive, but it depends heavily on assumptions about human physiology and machine performance.
Blood testing avoids some breath-related assumptions, but it introduces biological variability, handling risks, and laboratory uncertainty.
In many cases, blood testing is treated as stronger evidence simply because it sounds more scientific. That perception is not always justified.
For a general discussion of why chemical test results are often treated as more reliable than they should be, see:
Are Breath or Blood Tests in DUI Cases Ever Wrong?
Why the Type of Test Changes Defense Strategy
The type of chemical test used often determines:
- what records must be requested
- what scientific issues matter
- whether expert analysis is necessary
- how the case should be challenged
Breath test cases often hinge on machine diagnostics and testing conditions.
Blood test cases often hinge on documentation, laboratory practices, and statistical limits.
A lawyer who treats all OWI cases the same may miss issues unique to the testing method used.
What This Means When Evaluating a DUI Case
Many DUI cases are decided not by whether a chemical test exists, but by whether the test can withstand scrutiny.
When evaluating a Michigan OWI case, it is reasonable to ask:
- Does the lawyer understand both breath and blood testing?
- Do they know what records to request?
- Can they identify when a number is an estimate rather than a fact?
- Do they distinguish between breath-machine issues and laboratory failures?
Those questions often matter more than the charge itself.
To learn more about how to evaluate a DUI Lawyer, see: How to Choose the Best DUI Lawyer in Michigan | Michigan Drunk Driving Defense Lawyers
Frequently Asked Questions
Is Blood Testing More Accurate Than Breath Testing?
Not necessarily. Blood testing avoids some breath-related assumptions but introduces different scientific and procedural risks.
Can Breath Tests Be Challenged in Michigan?
Yes. Breath test challenges often involve machine stability, testing conditions, and physiological variables.
Can Blood Tests Be Wrong?
Yes. Blood tests can be affected by fermentation, improper handling, laboratory practices, and measurement uncertainty.
Does the Type of Test Affect the Outcome of a Case?
Often, yes. Defense strategy depends heavily on whether the case involves breath testing or blood testing.
Next Steps in a Michigan OWI Case
Whether your case involves breath testing or blood testing, the strength of the evidence depends on the science behind it.
At Barone Defense Firm, we evaluate OWI cases by examining how the test was conducted—not just the number on the report. Understanding the difference between breath and blood testing is often the first step in understanding the strength of the case.
To speak with an attorney, call (248) 306-9158 or 1-877-ALL-MICH (877-255-6424).
