Blood Alcohol Testing in Drunk and Impaired Driving Cases


What Are My Chemical Test Rights?

If you are arrested for impaired driving and will be subject to blood alcohol testing, the officer must inform you of your chemical test rights. The explanation will typically include a description of the consequences you will face if you refuse to take a chemical test, and of your right to obtain a blood or urine sample so you can conduct your own test. If the police fail to inform you of the consequences of refusing to take a chemical test, you may be able to challenge a suspension of your driver's license resulting from your refusal, and you may be able to keep the test result from being admitted into evidence during the prosecution of your case.

How Is My Blood Alcohol Measured By The Police?

In most states you have some degree of choice as to how your blood alcohol will be measured. For impaired driving involving the use of alcohol, you may be allowed to choose between a breath test and a blood test, and in some states you may be allowed to choose a urine test. Some states require the breath test, but allow you to demand a blood or urine test so you can verify the breath test results. If the police suspect intoxication from the use of medications or other drugs, you may be able to choose between a breath test and a blood test.

Breath tests are typically performed using a breathalyzer or a BAC Datamaster. A Datamaster is much less complicated to operate than the old breathalyzer machiens, that have largely been phased out. The old breathalyzer devices typically required that the officer read a needle that indicates a suspect's blood alcohol content, and it could be a very subjective determination if the driver blew a "0.09" or a "0.10". The Datamaster prints out a ticket with your mechanically determined breath test results, and no interpretation is required.

If you wish to be able to verify your sobriety, the best form of verification is a blood test. Urine tests are the least accurate measurement of your blood alcohol, as your urine often does not reflect your blood alcohol content at a particular point in time. However, if you believe that you are, in fact, over the legal limit, you may wish to gamble on urine testing, if your state grants you that option.

Can Blood Tests Be Inaccurate?

Obviously, lab testing errors can occur, which can render any test result inaccurate. However, the most significant concern for blood testing is whether the test is of the whole blood or of the blood serum. Police crime labs will test the whole blood, and will produce a "blood alcohol content" figure on that basis. However, many hospitals and clinics test only the blood serum, resulting in a blood alcohol content figure that can be 25% - 33% higher than a whole blood test result. A hospital may also use an alcohol swab before drawing the blood sample, which may contaminate the sample.

For impaired driving charges that involve allegations of intoxication from the use of medications or other drugs, a blood test may not be a good measure of impairment. Some people are tolerant of medications and drugs at a level that would leave others impaired. Also, the test may show use from many hours, days or in some cases weeks before, but still be presented as evidence of intoxication at the time of the traffic stop.

What Should I Tell The Police Before I Take A Breath Test?

The police will observe you for a period of time, usually about fifteen minutes, before administering the breath test, to make sure that you have not vomited or put anything in your mouth that might affect the test result.

  • If you are diabetic, athsmatic, on ulcer medications, or on a number of other medications, you need to tell the police what medications you are taking, and make sure that they write down the list.

  • Certain medical conditions and medications can interfere with the accuracy of your breath test, raising the resullt.

  • You need to tell the police if you have any sores, wounds, or infections in your mouth. If you are bleeding into your mouth, your breath test result will be artificially inflated.

  • You need to tell the police if you have vomited, even you taste just a little bit of vomit in your mouth. If you still have alcohol in your stomach, even a tiny amount of vomit can substantially increase your "breath test" result. (Even burping or hiccoughing can bring alcohol up from the stomach.)

  • You should indicate if you have any dental bridges or caps, which might be trapping alcohol inside your mouth.

What Happens If I Refuse To Be Tested?

If you do not take a mandatory test you will face driver's license sanctions, typically involving adding points to your driving record, and the suspension of your license, under your state's implied consent law. The police may also seek a search warrant, allowing them to take a blood sample for testing. The blood sample will normally be drawn by a professional, and blood sampling usually occurs at a clinic or hospital, but some states have trained police officers to draw blood from impaired driving suspects. In some states, refusing an alcohol test is a criminal offense, separate from the drunk driving offense.

Are There Times When I Should Refuse To Be Tested?

Test refusal is a controversial issue, and depends very much upon you r situation, your prior record, and the laws of your state. In some states, some attorneys caution drivers with histories of drunk driving offenses that they may be better off refusing to take an alcohol test than by cooperating. The rationale is that the driver will be better able to defend himself against drunk driving charges if the police don't know his blood alcohol, and that the severe consequences of being convicted as a habitual drunk driver outweigh the mandatory license suspension associated with refusing to take an alcohol test. It should be remembered that the police may apply for a search warrant to obtain a blood sample for testing, if a breath test is refused.

Test refusal is not a decision to be made lightly. It is so dependent upon state law, and an individual's driving record, that it is best made after consulting with an attorney. You can do a lot of damage to your driving record, and needlessly lose your license, if you make an ill-advised decision to refuse testing.

What Is "Implied Consent"?

Implied consent is the principle that, by driving your car on the public roadways, you agree to take chemical tests, such as a blood, breath or urine test, if you are arrested as an impaired driver. If you refuse to take a test after being arrested, the state can add points to your driving record and administratively suspend your driver's license for your refusal - even if you are not charged with drunk driving, or are acquitted.

Copyright © 2000 Aaron Larson, All rights reserved. No portion of this article may be reproduced without the express written permission of the copyright holder. If you use a quotation, excerpt or paraphrase of this article, except as otherwise authorized in writing by the author of the article you must cite this article as a source for your work and include a link back to the original article from any online materials that incorporate or are derived from the content of this article.

This article was first published on Mar 1, 2000, and was last reviewed or amended on May 26, 2016.