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What Is Blood Alcohol Concentration (BAC) 

Blood Alcohol Concentration (BAC) determines how intoxicated someone gets from drinking alcohol. It is the ratio of alcohol to blood in the body. The rate represents the percentage of concentrated alcohol in a person’s bloodstream. The percent is calculated by measuring the amount of alcohol in milligrams per 100 milliliters of blood. For example, a BAC of 0.20 means that a person’s blood supply is .2% alcohol. If the level of BAC is 0.10, then .1% of the bloodstream is composed of alcohol.

How Is Blood Alcohol Concentration (BAC) Measured?

The best-known method for measuring BAC is by using a breathalyzer. A breathalyzer measures BAC through breath samples. Authorities commonly use it during traffic stops or in criminal investigations and accidents. Unfortunately, if not maintained and calibrated regularly, breathalyzers can be inaccurate. A much more precise yet less standard procedure is the blood sample test. It is normally used when an individual refuses to participate in a breathalyzer screening or cannot consent to one. A medical professional or trained officer draws an individual’s blood to obtain their BAC during a blood sample test.

There are other various ways of measuring BAC. The most common examples are:

  • Urine tests
  • Saliva swabs
  • Hair follicle tests

How It Works

As soon as an individual starts drinking, their BAC rises. On average, the body can process one standard American drink an hour. A typical American alcoholic beverage is either 6 ounces or contains 14 grams of sheer alcohol. 

According to the National Institute on Alcohol Abuse and Alcoholism, examples of standard drinks include:

  • 12 ounces of regular beer ~ 5% alcohol
  • 5 ounces of wine, ~ 12% alcohol
  • 1.5 ounces of distilled spirits (gin, rum, tequila, etc.) ~ 40% alcohol
  • 8 to 9 fluid ounces of malt liquor ~ 7% alcohol. 

Though many beers, wines, and liquors follow the American alcohol standards, there are exceptions. Different brands can vary in actual alcohol content. To honestly know how intoxicating a beverage is, always check the label or ask the bartender. 

What The Results Mean

Alcohol that is not processed by the liver travels throughout the bloodstream and is measured. The more a person drinks, the higher their BAC level climbs. For most people, one standard American drink will raise their BAC between 0.02 and 0.04. The larger the BAC, the likelier a person is to show symptoms of intoxication. 

For instance, a BAC level of : 

  • 0.03, Produces impaired judgment, vision, and multitasking.
  • 0.05, Slows reaction time, steering, and the ability to focus .
  • 0.08, Induces low balance, sight, and speech.
  • 0.10, Creates all of the symptoms from .08 plus incoherent thoughts.
  • 0.20, Generates confusion, vomiting, horrible balance, and loss of consciousness. 
  • 0.40, Is life-threatening and can lead to a coma or death. 

It is important to remember that the listed effects vary from person to person. Since everyone’s physiology and alcohol tolerance is different, it is challenging to assess BAC by counting drinks. The rate at which it rises is not the same for everyone. Instead, measuring BAC by breath, blood, or urine samples is the best method. However, please note that large amounts of unprocessed alcohol within the body can always cause behavioral changes, impaired judgment, and even death. Individuals should never guess their BAC.

Factors That Impact BAC

Every human being is unique, and that uniqueness leads to differences in BAC rates. Even though a group of friends may have the same amount of drinks at a bar, their blood alcohol concentration rates are likely to be different. 

Several factors impact BAC like: 

  • Weight
  • Sex
  • Metabolic rate
  • Type of alcohol
  • Body fat percentage
  • Whether food was eaten before drinking
  • Products that contain alcohol (breath mints or mouthwash)
  • Smoking
  • Age
  • Genes

It is important to note that though medical prescriptions and illicit drugs do not affect BAC, they change typical intoxication signs. 

Why Does It Matter?

Intoxication is the primary cause of car accidents in the United States. Police officers commonly use BAC to reduce traffic incidents if they suspect a person is driving under the influence. In the United States, the federal BAC limit is 0.08%. To legally operate a vehicle, a person’s BAC must be below 0.08%. If the officer discovers the driver is intoxicated, then they will issue a DUI citation.   

High levels of alcohol consumption are risky and dangerous. By understanding, recognizing, and monitoring how much you drink, you can avoid debt, incarceration, and tragedy. If you realize that you or a loved one are having a hard time putting down the bottle, there is hope. There are several excellent addiction treatment centers ready to support anyone prepared to commit to change. Contact a treatment provider today. 

  • Author: Suzette Gomez | Last Updated: October 6, 2021

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    Suzette Gomez

    Digital Content Writer

    Suzette Gomez earned her Bachelor of Science from the University of Central Florida. Her desire to help others led her to a Pre-medical track with a focus on psychological and social development. After graduation, she pursued her passion for writing and began working as a Digital Content Writer at Recovery Worldwide LLC. With her background in medicine, Suzette uses both science and the arts to serve the public through her writing.

  • Medical Reviewer: Deborah Montross Nagel

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