DUI Blood Testing in Michigan OWI Cases: How Reliable Is a Blood Test?

The Short Answer

In Michigan OWI cases involving blood draws, prosecutors often present the blood test result as an unassailable scientific fact. Blood testing is frequently described as the “gold standard,” particularly in cases involving accidents, hospital draws, or serious allegations.

In reality, a blood test is not self-validating. It is the product of a multi-step biological and chemical process that can fail at several points. How the blood was collected, preserved, stored, transported, analyzed, and reported all matter, and weaknesses at any stage can affect reliability.

At Barone Defense Firm, we do not accept a blood number at face value. We evaluate whether the science actually supports the allegation.

When Blood Testing Is Used in Michigan DUI Cases

Blood testing is commonly used when:

• police obtain a search warrant for a blood draw
• a person is transported to a hospital after a crash
• breath testing is unavailable or refused
• drug or mixed-substance impairment is suspected
• the case involves injury or enhanced allegations

Hospital blood draws raise distinct scientific and legal issues. If your blood was taken during medical treatment, this companion article provides important context:
Michigan DUI Blood Test at a Hospital

How Michigan DUI Blood Testing Works

Michigan forensic laboratories typically analyze blood samples using dual column headspace gas chromatography with flame ionization detection (GC-FID).

Despite its reputation, GC-FID does not test liquid blood directly. The instrument analyzes the vapor (headspace) above a heated mixture of blood and solvent. The reported alcohol concentration is therefore an indirect measurement that depends on controlled assumptions and laboratory conditions.

Accuracy depends on proper execution at every step, including:

• sample identity and integrity
• use and mixing of preservatives
• temperature control and storage
• chain of custody
• calibration and quality control
• analytical batch performance

Blood testing is not a single event. It is a process.

Whole Blood, Serum, and Why Hospital Results Can Mislead

Many Michigan OWI cases rely on hospital records rather than forensic laboratory testing.

Hospitals often report alcohol concentration in serum or plasma, not whole blood. Serum and plasma values are typically higher than whole blood values because they lack the cellular components that dilute alcohol concentration.

Using hospital numbers without a scientifically valid conversion, or applying an incorrect conversion, can result in a legally misleading BAC, particularly when the reported value is near a statutory threshold.

This issue arises frequently in hospital-draw cases and is one reason those results require careful scrutiny.

Fermentation: When Alcohol Is Created After the Blood Draw

Blood is a biological sample. If it is not handled with pharmaceutical precision, it can change after collection.

Blood kits contain preservatives designed to slow biological activity, but those preservatives are only effective if:

• the vial is properly mixed after the draw
• the sample is stored at appropriate temperatures
• transport and analysis occur without undue delay

If those safeguards fail, microbial fermentation can occur. Certain microorganisms consume glucose in the blood and produce ethanol as a byproduct, causing alcohol concentration inside the tube to increase over time.

When this happens, the reported BAC may not reflect the person’s actual alcohol level at the time of driving.

Measurement Uncertainty: Why a Blood Number Is an Estimate

Every scientific measurement has an inherent margin of error. In forensic science, this is known as measurement uncertainty.

A reported number without an accompanying margin of error is not a fact—it is an estimate. International laboratory standards require laboratories to understand and quantify this uncertainty.

As explained in a peer-reviewed Michigan Bar Journal article, when the lower end of a scientifically valid uncertainty range falls below the legal limit, the prosecution may fail to meet its burden of proof beyond a reasonable doubt:
Breath and Blood Tests in Intoxicated Driving Cases Why They Currently Fail to Meet Basic Scientific and Legal Safeguards for Admissibility – Michigan Bar Journal

Why the Entire Analytical “Run” Matters

A blood sample is not analyzed in isolation. It is tested as part of an analytical batch, often consisting of dozens of samples processed sequentially.

When evaluating a blood test, we examine the entire analytical run, including:

• whether a high-BAC sample was analyzed immediately beforehand (carry-over risk)
• whether calibration drift occurred over the course of the batch
• quality-control performance
• internal standard consistency
• chromatograms showing unexplained or overlapping peaks

These issues rarely appear on a standard lab report but may be revealed in the underlying data.

Laboratory practices and evidentiary reliability concerns in forensic blood alcohol testing are discussed in this Michigan Bar Journal analysis: Understanding quantitative blood alcohol testing in drunk driving cases.

Why Waiting for Blood Test Results Can Hurt Your Case

Many OWI cases stall while blood results are pending. People often assume they should wait to hire a lawyer until the results are back.

That can be a mistake. Evidence preservation, early investigation, and strategic decisions often occur before results are released, especially in crash cases or hospital draws.

If your case is waiting on blood results, this article explains why early representation matters:
My Michigan DUI Case Is Waiting on Blood Test Results. Do I Need to Hire a Lawyer Right Away?

Frequently Asked Questions

Next Steps in a Michigan DUI Blood Test Case

Blood testing cases are science-driven and document-heavy. The outcome often depends on whether your lawyer knows what to request, how to interpret it, and how to challenge unsupported conclusions.

At Barone Defense Firm, we evaluate blood testing from collection through laboratory analysis. We do not assume the reported number is correct, we verify whether the science supports it.

To speak with an attorney, call (248) 306-9158 or 1-877-ALL-MICH (877-255-6424).