Is it better to take a blood or a breath test after a Colorado DUI?

Posted on June 12, 2019

There is no right or wrong answer. Both the Colorado DUI breath test and the Colorado DUI blood test have pros and cons in Colorado DUI cases, as discussed below.

People who are arrested for drunk driving in Colorado may elect to take a breath or blood test. Whatever the suspect chooses to do, people arrested for drunk driving are advised to be polite and cooperative with the police. How an arrestee reacts during this period can come in as evidence should the case go to trial.

Breath tests

There are four main advantages to choosing the breath test following a Colorado drunk driving arrest:

1. breath tests take much less time than giving blood;
2. blowing into a breathalyzer is a lot less invasive than submitting to a blood draw;
3. giving a breath sample is relatively painless, whereas giving blood can hurt — especially if the phlebotomist has trouble finding a vein; and
4. as discussed below, every person has his/her own “partition ratio”

Obviously, breathalyzers do not measure the amount of alcohol in blood. Instead, breathalyzers arithmetically convert whatever trace amounts of alcohol may be in the suspect’s breath to an equivalent blood alcohol content (BAC) number. This is known as a “partition ratio.”

Colorado police rely on the partition ratio of 2,100 to 1. Therefore, police assume that 2,100 milliliters of alcohol in a suspect’s breath means that there must be at least 1 milliliter of alcohol in his/her blood.

However, this 2,100:1 ratio is nothing more than an average. Everyone’s lungs absorb alcohol from their blood at different rates from each other. And not only do people’s partition ratios differ from each other’s — they can change day to day and fluctuate according to the person’s body temperature and the room temperature.

As opposed to some other states, Colorado law permits DUI defendants to introduce evidence of how different people have unique partition ratios. This evidence could help convince a jury to find reasonable doubt and acquit the defendant, especially if his/her BAC was near the legal limit and the state has no other evidence that the defendant was intoxicated.

Blood tests

There are three main advantages to choosing a blood test following a Colorado drunk driving arrest.

1. Blood tests are usually more accurate than breath tests;
2. Blood tests are confirmed by two different methods; and
3. Defendants may submit their blood samples for independent testing

Since blood testing is necessarily more complex than operating a breathalyzer, there are a lot more opportunities for the state to contaminate or otherwise invalidate the sample. Just some possible mistakes the state may make that defendants can raise as a defense include:

• The police failed to draw the blood within two (2) hours of the traffic stop;
• A person who was not a qualified medical professional performed the blood draw;
• The state failed to store the blood samples at the correct temperature;
• The state failed to send out the blood samples on time;
• The laboratory did not have proper certification;
• The state failed to retest the blood; or
• The state made errors in labeling the blood.

In addition, there is always a lag time between when the suspect is pulled over and when he/she is ultimately tested. In many cases the driver’s BAC was perfectly legal while he/she was driving because the alcohol in his/her system was not fully absorbed; then the BAC went over the limit later on during the testing. This “rising blood alcohol” phenomenon could be an effective defense to DUI charges.

About the Author

Neil Shouse

A former Los Angeles prosecutor, attorney Neil Shouse graduated with honors from UC Berkeley and Harvard Law School (and completed additional graduate studies at MIT). He has been featured on CNN, Good Morning America, Dr Phil, Court TV, The Today Show and Court TV. Mr Shouse has been recognized by the National Trial Lawyers as one of the Top 100 Criminal and Top 100 Civil Attorneys.