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What is BAC? (Blood Alcohol Concentration)

If you’ve ever had a drink or two and gotten behind the wheel of a car hoping for the best, you may want to understand how law enforcement measures your blood alcohol level (BAC). Your blood alcohol level determines how much your drinking is likely affecting your brain and reflexes. The law in North Carolina sets the limit for driving at .08 BAC. Let’s look at what exactly BAC is and how law enforcement may determine yours.

Factors to Consider

If you have a few drinks with dinner out and want to drive home, you must consider a couple of crucial factors influencing your blood alcohol level.


First off, men and women metabolize alcohol differently, so when considering whether you had too much to drink, consider your gender at birth. Men metabolize alcohol faster because they have highly active forms of ADH enzyme in their stomach and liver. (1)


To estimate your BAC, you also must consider your weight. A woman at 180 lbs who has two drinks with dinner might be legally capable of driving, while another woman weighing 145 lbs may not. Considering metabolism and weight, a male weighing 280 lbs can likely consume many more drinks than a female weighing 120 lbs.

Impaired Performance

Sometimes it is difficult to know when your alcohol level is above a safe level to drive. You’re just out having a good time and feeling good. Maybe you don’t even feel like you’ve been drinking. If you don’t have any physical effects from the beers you had with dinner, you might not even describe yourself as “having a buzz.”

However, if you drive a vehicle with an alcohol concentration of 0.08 or higher or while impaired by other substances, law enforcement may charge you with a DWI. If you are operating a commercial motor vehicle, you can face DWI charges at only .04 BAC. Underage drinkers face DWI charges with any amount of alcohol in their system.

Refusing Breathalyzer Testing

A law enforcement officer may ask you to take a breathalyzer test if they arrest you for suspicion of DWI. If you refuse to submit to a breathalyzer test, your license can be immediately suspended for at least 30 days and then up to one year for refusing the test. These consequences stand whether or not a court convicts you of DWI.

However, you may call a witness to come and be with you as a witness while you take the breathalyzer test. The test administrator (law enforcement) must wait up to 30 minutes for your friend or attorney to arrive to witness the test. You should use this 30 minutes to try to contact someone and ask law enforcement to wait the entire 30 minutes before submitting to a test of your breath. 

NC Law also states that an officer may ask you to take a second breathalyzer test. Your BAC is only admissible in court if the difference between the two numbers is not more than .02. Only the lower number in your sequential breathalyzer tests proves your level of intoxication. If you have already provided one breath sample, it is in your best interest to provide a second. Further, if you provide the first test and then refuse the second, law enforcement may admit the first test results. 

Refusing Chemical Testing

Law enforcement may also request chemical testing of blood or other bodily fluids instead of administering the breathalyzer. They can also request chemical testing in addition to the breathalyzer test. 

If you willfully refuse chemical testing, but the law enforcement officer believes that you exhibited impaired driving due to an alcohol-related offense, they may request a warrant to obtain a blood sample from you. 

Your charges still stand if officers don’t get a blood sample from you because of your refusal. The judicial system will not dismiss your charges, and you may not appeal for this reason.

Other Drug Testing

Taking illegal or inappropriate amounts of drugs that affect your ability to drive is also unlawful. Law enforcement officers may give chemical tests that identify other substances in your system after arresting you when you arrive at the police station.

The Department of Health and Human Services keeps a published list of permits issued for each qualified individual to perform analysis, the type of instrument they are authorized to perform tests on, and the date the permit was issued. 

According to the list of licensed chemical analysts published by the NC Department of Health and Human Services, some of the chemical tests available for blood testing in North Carolina may include: 

  • Gas Chromatograph
  • Gas Chromatograph w/ Headspace Autosampler
  • Shimadzu LC/MS-MS 
  • Agilent Technologies GC/MS
  • ELISA Tecan Freedom EVO 75 and 150 
  • Waters Acquity Xevo TQD Liquid Chromatograph
  • Tandem Mass Spectrometry
  • Varian 3800 Gas Chromatograph w/ CTC Headspace Autosampler 
  • Hewlett-Packard GC/MS (6890/5973) 
  • Agilent Technologies GC/MS EMIT 

We Can Help

If you’re facing DWI charges, our experienced DWI criminal law attorneys can help. Our experience as a former prosecutor brings a formidable team to your side. We examine state permits for any testing, whether law enforcement violated your rights, and if the evidence is admissible. Don’t go through this kind of battle without a knowledgeable attorney by your side. Contact us today to find out how we can help.