Watch How Antiseptic Swabs Can Cause BAC Blood Test False Positives By Andrew Mishlove on December 20, 2023

A vial of blood for a blood test

Blood tests are considered an accurate way of measuring a person's blood alcohol concentration (BAC). On the surface, they seem more reliable than breathalyzer tests and urine tests. However, errors in handling, storing, and analyzing the blood sample could lead to false positives in operating while intoxicated (OWI) cases.

These kinds of mistakes can happen the moment a needle makes contact with the skin. That's why lawyers must examine the methods that law enforcement and phlebotomists use to draw blood.

Here's a video that demonstrates how long it takes antiseptic swabs to dry and how that can affect blood test results.

A Breakdown of What We Just Watched

To restate the points in the above video, here is a breakdown.

Medical Blood Draws Are Different from Legal Blood Draws

A medical blood draw kit contains an ethanol swab to disinfect the skin. Since ethanol is a type of alcohol, different types of disinfectant swabs are used in legal blood draws to check a person's BAC.

A legal blood draw kit will often contain a Betadine (povidone-iodine) antiseptic wipe. This is a water-based disinfectant.

Betadine Swabs Take Significantly Longer to Dry Than Ethanol Swabs

If you disinfect the skin with an ethanol wipe, it takes about 30 seconds to dry. That's fast.

If you disinfect the skin with a Betadine wipe, it takes almost three times as long. Looking back at the video, it took about 1 minute and 20 seconds for my skin to be dry.

A phlebotomist needs to wait until the skin is dry before they can proceed with a blood draw.

There Is a Risk of Blood Sample Contamination from the Betadine Swab

If a phlebotomist draws blood before the skin is dry, there is a risk of contaminating the blood sample with Betadine and other substances on the skin that were not properly cleaned off.

While Betadine is a water-based disinfectant, there is a chance this contaminant could lead to an incorrect result in a blood-based BAC test.

Phlebotomists Are Used to Medical Blood Draw Swabs Rather Than Legal Blood Draw Swabs

Since phlebotomists are used to the 30-second drying time associated with ethanol swabs, there is a chance they may draw a blood sample prematurely when using a legal blood draw kit.

Ultimately, focusing on scientific and procedural minutia like this could help you with your OWI case.


Lab technician at a microscope taking notes

Other Kinds of Blood Test Errors

Betadine contamination is just one of many potential mistakes that could lead to false positives in a blood test. Here are a few other potential mistakes that could lead to errors in BAC testing.

Problems With the Blood Test Kit Itself

As pointed out in the video, the vials in a legal blood test kit each have expiration dates and lot numbers. If law enforcement uses an expired test kit or a defective test kit, it could lead to inaccurate BAC results.

Mistakes in Collecting the Blood Sample

In addition to drawing blood while a person's skin is still wet, a phlebotomist could be using contaminated gloves while handling the syringe or touching the skin. In these cases, a phlebotomist might use an ethanol-based hand sanitizer and then touch the outside of the gloves. Trace amounts of ethanol in the blood sample could be enough to affect the BAC.

Improper Handling of a Blood Sample

After the blood is collected, a number of mistakes could compromise the integrity of the blood sample. A vial that is improperly sealed could introduce all manner of contaminants that lead to incorrect BAC results. Vials that are labeled incorrectly or mixed up could lead to false positives and the wrong evidence being used against you.

Issues With When a Sample Gets Analyzed

A blood sample has a shelf life. As the blood decomposes, fermentation occurs. This leads to an elevated BAC in a blood sample. Many crime labs have a backlog of blood samples to analyze. While refrigeration slows down this process, it doesn't stop it completely. A stored blood sample may not accurately reflect your BAC at the time of the initial blood draw.


Wisconsin OWI attorneys Andrew Mishlove and Lauren Stuckert

How Testing Mistakes Can Help Us With Your OWI Case

There are many other variables to consider when it comes to OWI arrests. Mistakes by law enforcement and phlebotomists are just a facet of what happened. As we hear your story, we can consider how police and testing errors can be built into your defense strategy.

Creating Doubt in the Test Results

With so many potential errors stemming from a blood test, we can cast doubt on the BAC results. This isn't to undermine the legitimacy of forensic science, but a way to consider all of the variables that could be present.

An Informed Focus On the Science

Lauren Stuckert and I carefully consider how scientific evidence is presented in your case. We both have special training when it comes to the science of BAC testing.

  • Lauren received a certificate in Forensic Chromatography Blood Alcohol Analysis from the American Chemical Society at Axion Laboratories in Chicago. She was the first Wisconsin lawyer to receive this certification. She also completed the Forensic Solid Drug Analysis course through the American Chemical Society.
  • I am the developer and course director for blood analysis courses at the Shimadzu Laboratory at the University of Texas-Arlington. I also have special training in blood, breath, and urine testing from the National College for DUI Defense, and have previously taught other defense attorneys about this specialized field of forensic science.

Human Error Is Just One Part of Your Story

Human error and procedural mistakes are just one part of your story. We rely on storytelling when we defend clients.

In addition to pointing out flaws in testing, we will also humanize you for the jury so they see you as a person with similar values and struggles.

Need to Speak with an OWI Lawyer?
Contact Us for a Free Consultation

If you've been charged with an OWI in the state of Wisconsin, you need an attorney on your side who understands science, procedure, and the importance of crafting a compelling narrative in court. We are board-certified OWI defense attorneys with the forensic knowledge to back up our claims.

To request a consultation, contact our law offices today. We have offices in Milwaukee, Waukesha, West Bend, and Oshkosh.



Andrew Mishlove

About Andrew Mishlove
A board-certified OWI defense specialist, Andrew Mishlove has practiced law in Wisconsin since 1981. He is a nationally recognized figure when it comes to drunk and intoxicated driving defense. Mr. Mishlove is the author of Wisconsin OWI Defense: The Law and Practice and is on the Board of Regents of the National College for DUI Defense (NCDD).

Read Mr. Mishlove's Full Bio | All Posts by Mr. Mishlove

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Andrew Mishlove and Lauren Stuckert

Mishlove and Stuckert, LLC Attorneys at Law

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