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Blood Alcohol Concentration (BAC) Testing and DUI in Arizona

(Last Updated On: October 23, 2018)

Blood Alcohol Concentration (BAC) Testing and DUI in Arizona


Law enforcement officers in Arizona may use blood, breath, and urine tests to determine your blood alcohol concentration. The officer might also give you field sobriety tests.

We are often convinced that a lab or chemical test is always going to be accurate. You may feel that there is little hope of challenging the results of a blood, breath, or urine test that shows your blood alcohol concentration is over 0.08 or that you are under the influence of drugs. Just because you’ve tested for BAC higher than legally allowed, it’s important to remember that there may be issues in the testing process that will call into question the accuracy of a blood, breath, or urine test.


Understanding BAC Testing

When you drink alcohol it is absorbed into your bloodstream through your mouth, throat, stomach, and intestines. Unlike other food or drink, alcohol is not digested prior to going into your bloodstream. Alcohol is not changed chemically after it enters your body.


After you drink alcohol your body eliminates it through excretion (for example through your urine), evaporation (through your breath), or metabolic processes (through the liver).

The testing done by law enforcement is presented as very scientific and accurate. However, there can be significant issues with any BAC test.


Breath Testing

There are several types of machines that use breath to measure blood alcohol concentration. Some machines are portable and carried in the field by officers. This is often referred to as a preliminary breath test.


As alcohol goes into your blood stream it is carried through your lungs and over the membranes of your air sacs. Alcohol evaporates and when you exhale, alcohol is carried out with air from your lungs. The concentration of alcohol from your lungs is related to the concentration in your blood stream. The machine is intended to measure air from deep in your lungs.


Problems with Breath Testing

There are many factors that can affect breath testing. If you suffer from reflux or heartburn, it is possible that the breath test will result in higher BAC because reflux, burping, or regurgitation can cause an increase in the amount of alcohol in your mouth. This mouth alcohol may not be an accurate reflection of the amount of alcohol in your bloodstream.


An increase in mouth alcohol could also be caused by some over-the-counter medications, such as Nyquil. However, if you did take over-the-counter medications, they can cause impairment and be used in a case against you. If you sat down before testing, this could cause air to come up from the stomach and produce an inaccurate result. Even crying or vomiting before taking the breath test can impact the accuracy of the breath test.


The machine used to test BAC might also have issues that would create reasonable doubt in a DUI case. A machine might have been improperly maintained, calibrated, or handled by the officer. Even radio frequency interference might cause DUI testing machines to record inaccurate BAC readings.


Discussing the entire circumstances in your DUI case with one of our attorneys is important to ensure we provide you with the best defense. If you have dentures or bridgework or ate food that contained alcohol you could also experience an increased BAC over that which is in your bloodstream.


Blood Testing

Blood sample testing will measure the level of alcohol (or ethanol) in your blood. The two main types of testing are gas chromatography and enzymatic assay. Enzymatic testing produces results within about 20 minutes, while gas chromatography can take up to 8 hours. Enzymatic testing, though quicker, is less accurate than gas chromatography.


Often the officer involved in the stop will do the blood draw. In Arizona, the blood test kits include a vacuum tube that is coated with chemical preservatives and anti-coagulants. There are specific protocols that need to be followed by the person drawing blood to ensure accurate results. When the blood is drawn, you should also request a second vial so that you can conduct independent BAC tests.


Problems with Blood Testing

Blood enzymatic testing can produce problematic results with individuals that have certain physical conditions. For example, a person with diabetes may show a higher BAC depending on their blood sugar level. If rubbing alcohol was used to clean the skin prior to taking blood, this can contaminate the blood sample.


It is also possible that your blood sample was not preserved properly. As your attorney, we can request an independent test of your blood sample to ensure that it was not contaminated or preserved incorrectly. The retest might also reveal that you have an unusual blood condition that could have caused an inaccurate test result.


Urine Testing

Urine testing measures the amount of alcohol being excreted by your body. It is the least reliable for blood alcohol. Urine tests are done in 20-30% of cases. Officers will most often conduct a urine test if the breath test shows a lower BAC than might be indicated by your behavior. If the officer believes you to be more impaired than the breath test indicates, they may suspect drugs. Urine tests are also conducted when either the breath or blood test is not available for some reason.




Problems with Urine Testing

The procedures for a urine test include asking you to empty your bladder 20 minutes before a urine sample is taken for testing. A urine test will determine if you have any drugs in your system, but will not measure the amount of drugs. It is also possible for a urine test to show positive results for drugs that may have been ingested days before.


Some medication can show false positive results for illegal drugs. For example, Protonix specifically has a warning that persons taking it may test positive for marijuana. Over the counter cold medications may test positive for amphetamines. Just as in blood testing there are also issues related to how the urine sample is handled. If for example the sample is not stored at the proper temperature, it can ferment and actually produce alcohol in the sample.


Defending Against BAC Testing

In all of this discussion of BAC testing, it is important to remember that all testing is subject to inaccuracies. If after your arrest a blood, breath, or urine test results in a BAC over the legal limit or impairment you may feel as though you have no defense in your DUI case.


Our purpose in discussing testing issues and inaccuracies is to ensure that you understand the possible defenses in your case. At each step of testing for BAC, problems can occur that impact the accuracy of your test. This article has just touched the surface of the issues surrounding BAC testing in DUI cases.


The specifics of your case, any physical conditions, testing conditions, even environmental conditions present during the testing are important considerations when preparing your defense in a DUI case. Our attorneys are experienced in challenging BAC testing and providing you with the best defense possible. Contact our office for a consultation on your case.

Posted in Arizona DUI Law.


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