The Dirty Skin Defense

Posted by Jon Ibanez on September 15th, 2014

A few years ago, I assisted in a DUI trial where the jury acquitted the defendant partly because of the reasonable doubt raised by a defense expert who testified that the defendant’s “dirty skin” could have created a false positive blood test.

It would have been the defendant’s second California DUI conviction

Although I don’t remember the specifics of the stop or the DUI investigation, what I do remember is that the defendant opted for a blood test following his DUI arrest. When the results of the blood test came back, he was at a blood alcohol content level of 0.08 percent or slightly over.

The defendant took the case to trial.

Testimony at trial revealed that it took the prosecutor’s crime lab over a month to analyze the defendant’s blood. As the result of a backlog in cases, this is not an uncommon practice in Southern California county crime labs. This seemingly innocuous fact, opened the door for the defense to raise reasonable doubt that the defendant’s blood alcohol content was actually 0.08 percent or higher.

The defense introduced an expert witness to testify that, at the time the needle is injected into the arm to withdraw blood, it is possible that microorganisms located on the skin at the injection site can be extracted along with the blood sample into the vial. Although it is common practice for technicians who withdraw the blood to swab the injection site with hydrogen peroxide, contamination of the blood sample is still, nonetheless, possible. For obvious reasons, they don’t use rubbing alcohol to disinfect the injection site.

The expert further testified that, when analysis of the blood occurs a month or more after the blood is extracted, it is possible that the microorganisms which were extracted into the vial can cause the fermentation of glucose, which is a sugar, located in blood.

Simply put, fermentation occurs when microorganisms convert sugars into alcohol and carbon dioxide. I don’t need to tell you that this is the process by which people make the alcoholic beverages that we know and love.

Voila! The delay in crime lab’s testing of the blood allowed the stowaway microorganisms time to convert glucose in the blood sample into alcohol, thus producing falsely elevated blood alcohol content levels.

The prosecutor will argue that the blood vials contain a preservative, usually sodium fluoride, to preserve the integrity of the blood sample. However, studies have shown that sodium fluoride is ineffective against the most common microorganism, candida albicans.

Is the dirty skin defense enough to raise a reasonable doubt that a DUI suspect’s BAC was actually above a 0.08 percent?

While outcomes will vary on a case-by-case basis, it certainly was in the trial I assisted in.

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