How is BAC Determined in a DUI?

Blood alcohol content (BAC) is one of the most critical factors in a DUI case. It’s usually the number that leads to an arrest, and it is used by the prosecution to prove that you were in violation of the law. If your BAC was over .08, you were over the legal limit. But how is BAC determined, and can you fight BAC evidence when you know it’s wrong? When you are arrested for drunk driving in New York, your BAC is measured by breath or blood test. Both tests are quite fallible, but you’ll need the help of an experienced DUI attorney to refute the results.

Breath Test

The breath test measures BAC indirectly. Obviously, it measures the alcohol in your breath. To determine by your breath how much alcohol is in your blood, it needs a sample of deep lung air. Alcohol residue in your mouth and gases that have come up from your stomach, due to burping, hiccupping or vomiting, can throw the reading off. To prevent false readings, the machine has a mechanism that helps it determine the difference between residual mouth alcohol and deep lung air. Additionally, there is an observation period before administering the test to make sure stomach vapors won’t be involved.

Obviously, both can fail. The officer may not abide by the observation period and the machine may not properly detect the difference between mouth alcohol and deep lung air.

Blood Tests

A blood test should be more accurate, but many things can still go wrong. Human error during the blood draw itself, storage and transportation of the sample can all lead to false results. The blood must be drawn by a trained and certified professional. The wipe used to clean the area cannot contain alcohol. The right amount of preservative and anticoagulants must be used.

You have the right to have your blood sample tested by and independent laboratory to look for mistakes.

Timing and Chain of Custody

Improper timing can also make the BAC wrong. If the tests are administered too late, it can mean that you were not intoxicated at the time you were driving. Additionally, your DUI attorney will look at chain of custody to determine who had access to your sample and if it may have been handled improperly.

If you have been charged with DUI, McPhillips Fitzgerald & Cullum LLP, can help. Please call or email us today to schedule your free initial consultation.


Contact Our Firm Today

* All indicated fields must be completed.

Accessibility Toolbar