Challenging a DWI Blood or Urine Test in Minnesota

First Question: Did Police Need a Warrant?

Before reaching the science, there's a threshold legal question. Under current Minnesota law, a blood or urine test generally requires a search warrant (or a recognized exception). If police obtained a blood or urine sample without a warrant and without a valid exception, the result may be subject to suppression — and refusing a warrantless blood or urine test is not a crime. (See our DWI chemical-testing page for the breath-vs-blood-vs-urine rules.) This warrant issue is often the first and most powerful challenge.

How the Tests Actually Work

In Minnesota, blood and urine samples are typically analyzed at the Bureau of Criminal Apprehension (BCA) laboratories using gas chromatography (specifically, gas headspace chromatography). In simplified terms, the technique separates the components of a sample as they pass through a column at different rates, and a detector measures the alcohol present, producing a chromatogram the analyst uses to calculate the alcohol concentration.

The science is well-established — which is exactly why challenges need to be specific rather than a scattershot attack. The most effective approach targets the particular weaknesses in your case (the "rifle," not the "shotgun").

Challenging Urine Tests: The "First-Void" Problem

Urine testing has a distinctive vulnerability. Minnesota labs often test a "first-void" urine sample — the first urination after arrest — without having the person empty their bladder first. The concern: urine pools in the bladder over time, so a first-void sample can reflect alcohol accumulated earlier, and may not accurately correspond to the person's alcohol concentration at the time of testing (or driving).

• Minnesota courts (in cases like Edstrom and Tanksley) have generally held that gas headspace chromatography on urine is scientifically accepted and that first-void testing can survive a reliability challenge.
• But the correlation between a urine alcohol reading and actual impairment — or blood alcohol concentration — remains a legitimate area to attack, particularly on how much weight the result deserves.
• And remember the threshold issue: urine testing now generally requires a warrant, so the science question often comes after the warrant question.

Your Right to Confront the Analyst

This is a powerful and recently strengthened protection. Under the Confrontation Clause, the prosecution generally cannot simply hand the jury a lab report — the defendant has the right to cross-examine the analyst who did the testing (from Melendez-Diaz v. Massachusetts and Bullcoming v. New Mexico).

The U.S. Supreme Court reinforced this in Smith v. Arizona (2024): the state cannot get around confrontation by putting a "surrogate" analyst on the stand — someone who didn't do the testing — to relay the original analyst's results, even if framed as the "basis" for the surrogate's own "independent opinion." If the testing analyst's statements come in for their truth, the defendant has the right to confront that person.

What this means for you: If the analyst who actually tested your blood or urine doesn't testify — and instead a stand-in tries to sponsor the result — that can be a serious constitutional problem with the state's evidence. This is one of the most important modern tools for challenging lab-based DWI cases.

Chain of Custody and Foundation

Even a scientifically sound test can be challenged on how the sample was handled. The prosecution must lay a proper foundation and account for the chain of custody — the documented handling of the sample from collection through testing. Issues can include:

• Gaps or errors in who handled the sample and when;
• Problems with collection, preservation, storage, or labeling (for example, the preservative, refrigeration, or timing);
• Deviations from the lab's standard procedures; and
• Calibration or maintenance issues with the testing equipment.

Importantly, these evidentiary challenges apply in the criminal case under the Minnesota Rules of Evidence regardless of what happened in the civil license proceeding.

Criminal Case vs. Civil License Hearing: A Key Distinction

The rules aren't identical across the two tracks. For example, the strict list of who is qualified to draw blood under the civil implied-consent law does not automatically bar a blood test in the criminal case — Minnesota courts have held that criminal admissibility is governed by the Rules of Evidence (foundation, chain of custody, reliability), not the civil implied-consent qualifications. So a test thrown out in a license hearing isn't automatically out of the criminal case, and vice versa. Each track has to be fought on its own terms.

Physical Inability to Provide a Sample

If you agreed to a test but couldn't physically provide a sample, that situation has its own rules — and genuine physical inability is different from refusal. We cover this in detail on our DWI chemical-testing page.

Common Ways to Challenge a Blood or Urine Test

• No warrant (or no valid exception) for the blood/urine draw;
• Confrontation — the testing analyst didn't testify, or a surrogate was used (Smith v. Arizona);
• Chain-of-custody or foundation defects;
• First-void urine reliability and correlation to impairment;
• Equipment calibration/maintenance problems;
• An unlawful stop or arrest tainting the test (see our traffic-stops and DWI-arrest pages).

Key Terms

• Gas chromatography: The lab method used to measure alcohol concentration in blood/urine.
• First-void urine: The first urination after arrest — a sample with a known reliability critique.
• Confrontation Clause: Your right to cross-examine the analyst who tested your sample.
• Surrogate analyst: A stand-in who didn't do the testing — generally cannot sponsor the result (Smith v. Arizona).
• Chain of custody: The documented handling of the sample, which must be properly established.