How the Police Choose Between Blood and Breath Tests

Posted on August 15, 2023 in Blood Alcohol Tests,Breath Alcohol Testing,DUI

If a police officer believes a driver is operating a motor vehicle under the influence of drugs or alcohol, he or she can arrest the driver on suspicion of violating Arizona’s driving under the influence (DUI) laws. Before an arrest is made, the officer may require the driver to participate in a blood or breath test. An officer chooses which test to use based on the situation.

Breath Tests Are the Most Common in Arizona

It is up to the police officer who conducts the traffic stop to decide which type of DUI test to use to determine whether or not a driver is intoxicated. Breath tests are generally the first choice, as they are the simplest and least invasive testing method to use in the field. A breath test – commonly known by the popular brand name “breathalyzer” – refers to a handheld device that analyzes a driver’s breath after the driver blows air into it. 

A breathalyzer test measures a driver’s estimated blood alcohol content (BAC) by calculating the amount of alcohol present in the driver’s breath. Since alcohol is not digested upon absorption, some of it moves across the membranes of the lung’s air sacs. Detecting the concentration of this alcohol in the breath can determine the driver’s BAC using a ratio, since alcohol concentration in the breath is related to its concentration in the blood.

In Arizona, a BAC at or above 0.08 percent is grounds for an arrest for DUI “per se,” meaning the driver has tested over the legal limit, regardless of whether the driver appears impaired. However, it is possible to be arrested for a DUI with a BAC below 0.08 percent if the officer sees other signs of impairment. Arizona is also a Zero Tolerance state for underage drivers, meaning a driver under the age of 21 could get arrested for a DUI with any amount of alcohol detected in a breath test.

When Might a Police Officer Use a Blood Test Instead?

A blood alcohol level test uses a sample of the driver’s blood to measure the amount of alcohol present. This is a more direct way to calculate the driver’s BAC than a breath test; however, it is used less often due to the inconvenience and invasiveness of drawing a driver’s blood during a DUI investigation. This testing method will typically only be conducted over a breath test in the following scenarios:

• The breathalyzer testing device needs repairs or has not been calibrated.
• The initial breath test came up negative for alcohol but the officer suspects drug intoxication.
• The suspect has refused to participate in the breath test.
• The suspect is not a good breathalyzer test candidate due to issues such as medical conditions, vomiting or chewing tobacco in the suspect’s mouth.

Drivers in Arizona legally cannot refuse to comply with a request for a breath or blood alcohol test. Under Arizona’s implied consent law, motor vehicle drivers automatically give their consent to alcohol and drug tests when they receive their driver’s licenses. Refusing to give your breath or blood (or urine, if a urine test for alcohol is collected) will automatically result in the suspension of your driver’s license for one year under the implied consent law.

Can You Fight Against the Results of a Blood or Breath DUI Test?

Yes, it is possible to fight against the results of a blood or breath alcohol test during a DUI case. For example, your DUI defense attorney in Arizona may be able to argue against the validity of the test results with evidence such as improper breathalyzer device calibration, an equipment malfunction or issues with how the officer conducted the test. It may also be possible to have blood alcohol level evidence ruled inadmissible if it was obtained during an illegal search and seizure.

Contact an attorney at Rosenstein Law Group for more information about test results if you have been arrested for an alleged DUI in Arizona.