CO Blood or Breath Test After DUI: Which Is Better?

When you are pulled over for a DUI, you may expect to get a breath test by the police. This will test your blood alcohol content and demonstrate if you are above the legal limit of 0.08 percent. But what many people don’t know is that you can also opt to have a blood test done to determine your blood alcohol content.

Which is better: blood or a breath test? The truth is, there is no wrong or right answer to this question. Both a breath test and a blood test have good and bad aspects to them when you’re facing a DUI.

Here is what you need to know about blood and breath tests in Colorado. We will help you understand the differences as well as which one may be the right one for you – in case you ever need to know!

Breath Tests

There are pros and cons to a breath test for alcohol if you are suspected of a DUI in Colorado. The main pros to a breath test include that it is:

  • Faster and simpler than having a blood sample taken
  • Less invasive than having blood taken
  • Painless, especially for people who may have difficulty having blood drawn
  • Subject to your individual partition ratio, discussed in further detail below

What isn’t really understood by most people is that a breath test doesn’t really test the amount of alcohol a person has in their blood. Instead, what they analyze is the trace amount of alcohol in a person’s breath to what is an equivalent blood alcohol content. This is also called a partition ratio.

The problem is that the partition ratio used in Colorado by the police isn’t really the average. Every person’s body absorbs alcohol differently, including how it is absorbed in the lungs. People have different partition ratios, and they can change based on many factors, such as body temperature and even the temperature outside.

Colorado’s law allows a person to show evidence in court about unique partition ratios, which can help convince a jury that your blood alcohol content as measured by a breath test may not have been accurate. Introducing this element of reasonable doubt can help a case.

Blood Tests

There are certain advantages to choosing a blood test if you are pulled over for suspected drunk driving, such as:

  • They are far more accurate than a breath test.
  • They use two different methods for confirmation of results.
  • You can submit a blood test for an independent sample.

Obviously, blood tests are more involved than a breath test, and there are more opportunities for the sample to be contaminated or mishandled by the police in the process. There are problems faced by the police when collecting blood samples, too, such as:

  • Failing to draw the blood within an adequate timeframe
  • Failing to store the blood correctly
  • Having someone who isn’t’ qualified to draw blood take the sample

However, you can use these mistakes to your advantage in your defense should they occur.

Denver DUI Attorney


Probably the biggest disadvantage to a blood test is that it takes time between when you are pulled over and when you are tested. In that time, your blood alcohol content can actually go up. So, you could have been within the legal limit while driving but not when tested.

No matter which method you ultimately choose, if you’re facing DUI charges, make sure that you have an experienced lawyer on your side who can guide you through it.

About the Author:

Denver-based criminal defense and DUI attorney Jacob E. Martinez is a knowledgeable and experienced litigator with a record of success providing innovative solutions to clients facing criminal charges of any severity. Mr. Martinez has been recognized by countless legal organizations for his exemplary defense work, including Avvo, Best DWI Attorneys, Expertise, Lawyers of Distinction, The National Trial Lawyers, and others. He was also named one of the 10 Best in Client Satisfaction in Colorado by the American Institute of Criminal Law Attorneys for 2020, and is Lead Counsel rated.