Challenging Blood and Breath Test Results in North Carolina DWI Cases

Blood and breath tests are used to determine whether a driver is under the influence or not of alcohol and/or drugs. These tests are marketed as being accurate and easy to use. Sometimes they can be the decisive factor (1) in determining whether there is probable cause to arrest and charge a driver with a DWI, and/or (2) in a jury returning a guilty verdict at trial.

Breath and blood tests, however, are not without controversy. And failing one of these tests -- contrary to what you may believe -- does not mean an automatic conviction. You can challenge these tests. And you should challenge them.

If you have been arrested for a DWI charge, contact an experienced DWI attorney to learn more about how you can challenge the charge. In the meantime, here is a summary of how a defense can be made by challenging these test.

DWI Defenses in Shelby, NC

If you have been charged with a DWI, you can challenge it. Though each case is dependent on the circumstances and facts, a strong defense can still be built with the help of experienced North Carolina DWI lawyers. Part of this defense can include challenging chemical tests.

Challenging a Breath Test

A breathalyzer is used to take your breath test. You may use a portable breath test (PBT) at the site of the traffic stop. The PBT is a handheld device that provides a readout of your blood alcohol content but does not provide a paper printout like a non-portable breathalyzer instrument located at a police department or state trooper barracks.

There are two ways breath tests can be challenged: (1) admissibility; and (2) breath test errors.

Inadmissible Breath Tests

Inadmissible breath tests can be due to the administration of the blood test or overall maintenance of the machine. The admissibility of breath test results come down to four primary factors:

  1. Is the model recognized by the State as an approved device?
  2. Did the police properly read the chemical test refusal warning to you?
  3. Did the police properly administer the breath test on you?
  4. Was the breathalyzer instrument properly maintained and in proper working order?

If the officer failed to administer the test properly, to maintain the instrument properly, or read you the chemical test refusal warning, then the results could be inadmissible. To a lesser extent, if the model is not recognized by the State or the model was not in proper working order because it was not properly calibrated, the breath test results could also be deemed inadmissible.

Breath Test Errors

Breath tests can sometimes produce results in error based on the person's chemical composition when taking the test. Variables can factor into a false positive due. Dietary changes, non-alcoholic item usage, and pre-existing medical conditions can lead to false positives.

Examples of how breathalyzer tests may produce false positives due to:

  • An altered mood
  • An empty stomach
  • Ketogenic diet
  • Acid reflux and its side effects
  • Diabetes and hyperglycemia
  • Smoked cigarettes
  • Used mouthwash.

Additionally, certain asthma medicines contribute to breath test errors. Some of the medicines which have been alleged to result in false positives are:

  • Budesonide (used to treat allergies, Crohn's disease, hay fever, and other ailments)
  • Salbutamol (also known as albuterol; used to treat asthma and chronic obstructive pulmonary disease)
  • Salmeterol (used to treat asthma and chronic obstructive pulmonary disease).

Challenging a Blood Test

Blood tests, although generally more accurate than breath tests, can also be challenged. These challenges can be made for a number of reasons, including but not limited to the improper administration, improper handling of the blood sample, and improper chemical solutions.

Improper Administration

When blood samples are taken in DWI cases, police must either first obtain your consent to withdraw blood or obtain a warrant to do so. If a warrant was improperly obtained and executed, a constitutional violation may have occurred. If so, any evidence flowing from that violation can be deemed inadmissible by the court.

Improper Handling of the Sample

A blood sample will pass through many hands, and at any time, it is subject to contamination. When that happens, false positives can also happen.

For instance, the blood sample must be properly stored. Typically, a nurse or another technician draws blood from the suspect using a vacutainer. Each vacutainer has a specific expiration date. If the vacutainer expires, the quality is no longer guaranteed. Another storage issue occurs when the seal is faulty. A faulty seal reduces the integrity of the sample and may cause fermentation, which is the formation of alcohol in the blood and which can cause the results to produce a false positive.

Improper Chemical Solutions

Improper chemical solutions refer to the chemicals added to the test tube for proper testing, namely sodium fluoride and potassium oxalate. Both substances are added to the test tube when testing the blood, but if the proper amounts are not added, flawed results or false positives occur.

What Should You Do if You Have Been Charged with a DWI in North Carolina?

If you have been charged with a DWI in North Carolina, contact an attorney. So many people who have been charged with the same and who have tested positive for alcohol or drugs in their system believe those results mean the case is an open & closed case. But it's not. In fact, you can fight the charges successfully. A positive breath or blood test does not automate a conviction. When a strategy is developed by experienced lawyers to challenge the results through forensic and other scientific evidence, you stand a good chance of defeating the charge against you. So, if you are thinking of pleading guilty, don't. Contact a lawyer and plead not guilty then let the lawyer work to secure your rights and freedom.

Attorneys at Caulder & Valentine Law Firm, PLLC are experienced and know the law, the court system, and the defenses to DWI charges. They have the resources and legal minds to help you move toward a favorable outcome in your case. Contact us online or call us at 704-470-2440 to schedule a consultation.


Shelby Office
303 West Marion Street
Shelby, NC 28150
704.754.8401 (fax)
Gastonia Office
316 S Chester St
Gastonia, NC 28052
704.754.8401 (fax)