by the Phoenix DUI lawyers at Ariano & Associates, PLLC

blood test as one of the tests to determine bac in a dui explained by a phoenix dui lawyerThe road to a Driving Under the Influence (DUI) charge is a simple one that you do not want to go down. If you are pulled over because a police officer has reason to believe you are driving while intoxicated, you impliedly consent to field sobriety tests. There are a variety of tests the officer may be able to conduct to determine whether or not you are under the influence of a drug, drug metabolite, or alcohol. If these tests show that you have a blood alcohol concentration (BAC) of over 0.08% (or less in the case of a commercial vehicle), you will be arrested and charged with a DUI.

What types of tests can a police officer conduct to determine your BAC?

The most standardized chemical tests are blood, urine, and breath tests. There are other types of field sobriety tests that are used, but they have been sanctioned by the National Highway Traffic Safety Administration (NHTSA).1 The chemical tests will no doubt be more accurate than other field sobriety tests, but each has its own flaws depending on the circumstances.

Blood Tests

Police officers who suspect you of driving under the influence are allowed to take your blood to determine your BAC. You impliedly consent to these blood, urine, or breathalyzer tests the moment you get your driver’s license. Although the blood test is probably the most accurate of the three, there can be issues with the accuracy of your blood test. A lot depends on the manner in which your blood was collected (i.e. it could lead to a false positive if the specimen is compromised because of a lack of training) and the storage of the sample (i.e. circumstances surrounding long term storage may increase fermentation in the blood).2

Urine Tests

The urine test is arguably the least reliable type of sobriety test used today.3 This is because the presence of a drug or alcohol in the urine may not be reliable information as to whether you were actually under the influence at the time you were driving.4 Further, the percentage of alcohol in the urine may not be the same as the percentage in your blood.5

Breath Tests

The breathalyzer test uses your breath to determine whether or not you have alcohol in your system by converting the breath alcohol content to a standardized formula to determine your BAC.6 This test has been criticized for varying at least 15% from your actual BAC, which may lead to you being falsely convicted.7

The Horizontal Gaze Nystagmus

This tests works when the officer positions an object such as a pen or finger about a foot from the driver’s face and moves the object from one side to another while observing the driver’s eye movements.8 Nystagmus refers to the involuntary jerking or bouncing of the eyeball that occurs when there’s a disturbance of the inner ear system or the oculomotor control of the eye.9 Research shows that this test is the most accurate of the three, although there can be some technical errors.10 It has a 77% accuracy rating in detecting BAC of 0.10% and higher.11 

See more here.

The One Leg Stand

The one leg stand test is not as accurate as the horizontal gaze nystagmus. However, it is still used often. Here the officer will need to make sure he or she explains how the test works before actually asking you to perform it.  You will then be asked to stand with your feet together and arms together at your sides and then raise your leg roughly six inches above the ground.12 You are then asked to count from 1,000 to 1,030.13 It is important to note that before you begin the test, the officer should ask you whether or not you have any questions or doubts about the test.14 The NHTSA says that 84% of individuals who cannot maintain balance or put a foot down in this process will have a BAC of 0.08% or more.15 Of course, the test itself is not entirely accurate and a lot depends on your circumstances. For example, if you are over 65 or have certain physical impairments you should not be asked to do the one leg stand test.16

The Walk and Turn

This type of field sobriety test has two parts: the officer first explains and demonstrates what is to be done so that there is no confusion and then asks  you to place one foot in front of the other in a straight line with the heel of one foot touching the toes of the other; then, the officer will demonstrate and explain how you are to walk the straight line before asking you to take nine heel-to-toe steps down the line.17 The officer will look for several signs of intoxication, including starting before instructions are over, stepping off the line, failure to touch heel to toe, using arms to balance, and improper turning.18 According to the NHTSA, this test indicates that 79% of individuals who exhibit two or more of these mistakes will have a BAC of 0.08% or greater.19 However, circumstances may make the test inaccurate. For example, slippery or uneven surfaces or inadequate lighting may make you falter.10

If you have been arrested for a DUI and your BAC was over 0.08% because of one of these tests, you should contact an Arizona DUI attorney. Your attorney will be able to best assess your situation  and put forth your best defenses against any test inaccuracies.  Contact a dedicated Phoenix DUI lawyer at Ariano & Associates who are on call 24 hours a day, 7 days a week.

[1] Field Sobriety Tests: Standardized and Non-Standardized, fieldsobrietytests.org, http://www.fieldsobrietytests.org/(last visited Dec. 16, 2014).

2 Peter Johnson, Challenging the Blood Test In a DUI Case, dui.drivinglaws.org, http://dui.drivinglaws.org/resources/dui-and-dwi/dui-defense/challenging-blood-test-dui-case.htm (last visited Dec. 18, 2014).

3 Rich Stim, Why Urine Tests Are the Least Reliable DUI Chemical Test, dui.drivinglaws.org, http://dui.drivinglaws.org/resources/dui-and-dwi/why-urine-tests-least-reliable-bac.htm (last visited Dec. 18, 2014).

4 Id.

5 Id.

6 Breathalyzers Fail Legitimacy Test, motorists.org, http://www.motorists.org/dui/breathalyzers-fail-legitimacy-test (last visited Dec. 18, 2014).

7 David J. Hanson, breathalyzer Accuracy and DWI/DUI Conviction Rates, ww2.potsdam.edu, http://www2.potsdam.edu/alcohol/DrivingIssues/1093825780.html#.VJOxcV4Ac (last visited Dec. 18, 2014).

8 Horizontal Gaze Nystagmus: The Science & The Law, nhtsa.gov, http://www.nhtsa.gov/people/injury/enforce/nystagmus/hgntxt.html (last visited Dec. 16, 2014).

9 Id.

10 Horizontal Gaze Nystagmus, duifoundation.org, http://www.duifoundation.org/drunkdriving/testing/fieldsobriety/horizontalgazenystagmus.php (last visited Dec. 18, 2014).

11 Id.

12 One-Leg Stand, duifoundation.org, http://www.duifoundation.org/drunkdriving/testing/fieldsobriety/onelegstand.php (last visited Dec. 18, 2014).

13 Id.

14 Id.

15 Standardized Field Sobriety Testing, nhtsa.gov, http://www.nhtsa.gov/people/injury/alcohol/sfst/appendix_a.htm (last visited Dec. 18, 2014).

16 DWI One Leg Stand Test Accuracy, d-w-i.org, http://www.d-w-i.org/dwionelegstandtestaccuracy.html (last visited Dec. 18, 2014).

17 Walk and Turn, duifoundation.org, http://www.duifoundation.org/drunkdriving/testing/fieldsobriety/walkandturn.php (last visited Dec. 18, 2014).

18 Walk and Turn

19 Standardized Field Sobriety Testing, supra note 15.

20 Walk and Turn Test Defenses, walkandturntest.net, http://www.walkandturntest.net/ (last visited Dec. 18, 2014).