Making Sense of the Surprisingly Complex Science Behind DUI Blood Testing

Have you ever thought about what actually happens when the police draw blood as part of a DUI investigation? It’s much more complex and complicated than you might think.

In today’s post we’ll talk more about DUI blood testing, what makes accurate results so tricky, and how a DUI defense lawyer can use this information to their clients’ advantage.


Myth: Blood alcohol tests and drug tests are similar

Fact: there’s a big difference between testing for alcohol in the blood and testing for drugs in the blood.

The primary difference is that alcohol is a Volatile Organic Compound (VOC). Alcohol does evaporate, so a VOC is best tested on a scientific instrument called a Gas Chromatograph. This machine can detect and measure alcohol with the highest degree of accuracy.

Drugs, on the other hand, are Non-Volatile Organic Compounds (NVOC). Drugs do not evaporate. NVOC substances, like most drugs, are tested with an instrument called a Liquid Chromatograph. This instrument can detect and measure drug substances the best.

Marty Judnich, Montana DUI attorney observes the use of a liquid chromatograph.


What does chromatography do?

Chromatography equipment makes a preliminary “guess” of what substances are found in the blood (also known as eluding). The “eluding” process separates different substances from each other, identifying one apart from the other.

Once the chromatographic machine is finished with its analysis, it provides a chart showing the separation of substances.

Marty Judnich reviews the results of an initial chromatography chart


Here’s where things get tricky

Once the preliminary separation and analysis is charted, the second step of the analysis can begin.

A scientist must now choose from one of several options. Alcohol testing usually relies on a Flame Ionization Detector for the next step. This measures the amount of alcohol that was initially present in the blood.

However when testing for drugs (and sometimes alcohol) there are other testing options, including what’s known as a Mass Spectrometer.

Whoa, sounds fancy right? It is.

A Mass Spectrometer essentially breaks down different substances and measures the amount of those substances. This allows the instrument to differentiate between different types of substances and creates a very accurate profile of what is being measured.


What do the results look like?

Now, do all these fancy scientific machines tell you exactly what you’re looking at? No, they don’t.

Even with all this instrumentation, a human scientist must still be able to read the information coming out of these machines. They must compare them and essentially make a guess at what substance was found and how much of it was found.


That’s just the beginning…

DUI blood testing is very complicated and this article has just begun to scratch the surface. However, there’s one important takeaway from today:

Blood testing is, and always will, be a guess.

Scientists use test results to make a guess at what is found by a machine by comparing one thing to another.


The Judnich Law Office knows the ins-and-outs of DUI blood testing

As an experienced DUI defense attorney, I’ve studied the DUI blood testing process and understand the steps scientists take and the process by which they make their guesses.

Thanks to this background and knowledge, when representing my clients in Missoula DUI cases, I’m able to make sure that a blood test was conducted properly. More importantly, I’m able to discover problems in the blood testing process and the results, which can help your case.

For more information, contact the Judnich Law Office. Or give me a call at (406) 721-3354 for your confidential consultation.