Breath or Blood Test After a California DUI Stop?

Posted by Jon Ibanez on October 19th, 2017

Let’s imagine a common DUI scenario.

A person is stopped on suspicion of a California DUI. The person stopped has read my many posts telling readers that the field sobriety tests are optional and should not be submitted to. So they politely decline the field sobriety tests. Then the officer requests an on-scene breathalyzer known as the “preliminary alcohol screening” test or PAS test. In addition to my posts reminding readers that this too is option, the officer also informs the driver that the PAS test is optional. So this too is politely declined by the driver. Lastly, the officer advises the driver that they are under arrest on suspicion of a California DUI and that, by law, they must submit to a chemical test which can either be a breath or a blood test.

Which test should the driver choose? Breath or blood?

The DUI blood test is much more accurate than the DUI breath test. The blood test is far less likely than a DUI breath test to produce a false reading. Another benefit of a DUI blood test is that the law requires that a sample of the blood is saved for future testing by the DUI suspect’s defense attorney. The defense attorney can have the sample tested by its own blood analyst to contradict the results of the prosecutor’s analyst. This is called a “blood split” and it is commonly used in DUI defense.

The blood test, however, is not infallible. See my previous post:

The Dirty Skin Defense

Since the blood test is more accurate, if a person knows that they have not had much to drink and they are fairly certain that they are under the legal limit of 0.08 percent, then a blood test might be the better option. On the other hand, the blood test might not be the best for someone who is clearly over the legal limit because it will be more difficult to dispute the test results.

 Unlike the blood test, the breath test is rather unreliable. Breath tests can provide false readings for several reasons. See Lawrence Taylor’s post:

Are Breathalyzers Accurate?

Although California DUI attorneys cannot dispute the reliability of breathalyzers as a whole during a DUI trial, they can provide evidence that the particular breathalyzer used in an individual case was inaccurate.

Unlike the blood test, the breath test may be a better option for someone who knows they are likely over the legal limit because it will be easier for a California DUI attorney to refute the results. However, many people who are actually under the legal limit may still test over the legal limit because of the same inaccuracies.

Simply put, if you are fairly confident that your blood alcohol content will below the legal limit of 0.08 percent, you’re probably better off opting for the blood test because it will accurately show that you were, in fact, under the legal limit. However, if you think there is a chance that you could be above the legal limit, you might be better off opting for a breath test so that your attorney can challenge the results if you test above the legal limit.

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