Sober Driving 101: Medical vs. Legal BAC

If Susan has a medical BAC of .167 percent and Bob has a legal BAC of .08 percent, who can be charged with drunk driving?

Understanding blood alcohol concentration (BAC) probably isn’t the first thing you think of when you wake up. Unless, of course, you wake up with a pounding head and the vague memory of your intoxicated actions from the night before. If those memories include an arrest for drunk driving, your BAC may actually be a lot more important to you than you ever thought possible. Now you just have to figure out what all of those numbers mean for your future.

BAC is the measurement of ethanol (alcohol) in your blood:

• The higher your BAC, the more impaired you are.
• At a certain point, a really high BAC level can kill you.
• Legally, you are considered too intoxicated to drive when your BAC measures .08 percent or higher.

Your legal BAC is different from your medical BAC, which is where things can get confusing. This man’s BAC measured almost six times over the legal limit (.495 percent), but the hospital’s measurement was even higher at 0.604 percent. The difference between the two figures comes down to how the sample was obtained: through urine, blood or breath and the math that follows the method. Either way, the man was clearly over the limit and is very lucky to be alive today.

Despite the difference in BAC numbers, there is no difference between the effects of alcohol through either method. The BAC reading from a breathalyzer or ignition interlock device accurately shows whether the person submitting the breath sample is sober enough to drive, just like the higher number of a medical BAC would indicate the same. If you refuse the breathalyzer during a traffic stop, you will likely be compelled to submit a blood or urine sample for testing, where you’ll see the math difference in action.

Sadly, both Susan and Bob are over the BAC limit for safe, responsible driving and will face the consequences for drunk driving. You, however, can see that neither measurement is worth the study in BAC math and that you’re just better staying sober when you drive. That’s math that makes sense, no matter which method you use.