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What is Blood Alcohol Concentration (BAC)?

Blood Alcohol Concentration (BAC) measures the amount of alcohol (ethyl alcohol or ethanol) in an individual’s bloodstream. Shown as a percentage, BAC refers to the speed by which individuals absorb, distribute, metabolize, and get rid of the substance.

For example, if a person’s BAC is 0.08%, .08 grams of alcohol are present in every 100 milliliters of blood. 

If a person’s BAC is 0.02%, symptoms like partial loss of judgment, relaxation, mild body warmth, and mood changes can occur. 

The blood alcohol concentration will determine what effects the alcohol will have on the body. The liver is only capable of metabolizing approximately one standard alcoholic drink per hour. In many cases, one standard beverage means: 

  • 12 ounces (oz.) of beer
  • 5 oz. of wine
  • 1.5 oz. of whiskey 

If you have more than one drink within an hour, your BAC will be higher than that of someone who drank only one beverage within the same time frame.

Also, even if individuals stop drinking alcohol or are unconscious, BAC may not remain as a steady figure or go down. Because the body continues to let alcohol pass into the bloodstream, the BAC can rise in response and cause serious health signs or symptoms. 

The higher the BAC, the more intense (and sometimes more dangerous) effects of alcohol.  

In many cases, particularly in individuals who do not participate in chronic drinking, signs of intoxication will be evident based on BAC. Yet, tolerance built among individuals who suffer from chronic alcohol abuse could mask these signs.

To figure out someone’s BAC, doctors or law enforcement officials may use a breathalyzer or perform blood tests. A breathalyzer is a device that measures the amount of alcohol in the breath.

What is the Lethal Blood Alcohol Content Level?

According to the National Institute on Alcohol Abuse and Alcoholism (NIAAA), a blood alcohol content level between 0.31% and 0.45% can be life-threatening. 

When you reach these numbers, there is a significant risk of death due to the effects caused by drinking. 

Alcohol is a central nervous system (CNS) depressant. Extreme or excessive quantities of the substance can dramatically slow vital life functions such as breathing.   

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How Does Someone Reach This BAC Level?

Multiple factors can influence how the body absorbs and metabolizes alcohol. These factors also influence your BAC level: 

Amount of Alcohol (Number of Standard Drinks) 

As mentioned before, BAC depends on the amount of alcohol in an individual’s bloodstream. The liver is incapable of metabolizing more than one standard drink (14 grams of pure alcohol) in an hour. So, anything more than a standard alcoholic beverage within an hour will increase the BAC. 

People who binge drink or drink heavily will experience a spike in BAC:

  • In binge drinking, men have 5 or more alcoholic beverages in less than 2 hours, while women have 4 or more drinks within the same time frame. 
  • In heavy drinking, men have 4 or more alcoholic beverages regardless of the day, while women have 3 or more drinks.

Whether it be binge or heavy drinking, the high quantities of alcohol overwhelm the body’s metabolic processes, and BACs rise quickly. 

Gender

Because of biological differences, women have more trouble breaking down alcohol than men. This means that women will have increased BACS in shorter times than men. 

Three main reasons can explain why this occurs:

  • Body composition — compared to men, women have a higher body fat percentage yet lower water percentage. Alcohol accumulates in the bloodstream more often in women than in men because fat cannot dissolve the beverage. 
  • Stomach ADH — ADH (alcohol dehydrogenase) is an alcoholic-metabolizing enzyme that is more commonly found in men’s stomachs. Because of this, men can metabolize much more alcohol than women before the beverage reaches the bloodstream. 
  • Liver ADH — breaking down alcohol requires ADH in the liver as well. However, this process is not as efficient in women’s livers as in men’s, contributing to an increased BAC. 

Lastly, hormones play a role in alcohol metabolism. When women have their periods, BAC may be higher because of changes in hormones. 

Body Weight

Individuals' weight can define the amount of space by which alcohol diffuses in the body. For example, people who weigh 130 pounds could have two beers and a lower BAC than individuals who weigh less and drink the same quantity. 

Also, someone who has more muscle mass can absorb and break down alcohol more efficiently than those with a higher body fat percentage. Alcohol does not dissolve in fat. 

The accuracy of BAC tests can vary depending on when it was performed. A blood alcohol test provides the most accurate results when done within 6 to 12 hours after the last consumed alcoholic beverage. 

Body Size

Similar to body weight, body size can influence the speed of alcohol absorption and metabolism. Even if alcohol consumption remains the same, individuals with smaller body frames could have increased BACs than those with more sizable body frames.

Stomach Contents

A higher BAC can also occur if you drink on an empty stomach. If you know that you will be drinking alcohol, it is best to eat beforehand. Food high in protein can especially help lower alcohol processing in the body. Eating before drinking minimizes the likelihood of overwhelming the liver and reaching a dangerous BAC level. 

What BAC Level Causes Alcohol Poisoning? 

Individuals with a 0.0 percent BAC are sober and do not risk alcohol poisoning (otherwise known as alcohol intoxication). However, if the BAC level increases, the risk of alcohol poisoning also rises. 

At 0.08 percent BAC, an individual is legally intoxicated. In fact, in the United States, people with a 0.08 percent BAC or higher while driving can face criminal charges for drunk driving. In some states, like Utah, it is 0.05 percent. 

Alcohol poisoning could occur in individuals whose BAC levels fall between the range of 0.250-0.399 percent. At this point, you may lose consciousness, and the risk of death is extremely high. 

At least 2,200 individuals pass away from alcohol poisoning annually. 

Signs of Alcohol Intoxication (Poisoning) 

It is important to say that the effects of alcohol intoxication may not always be visible. For this reason, direct blood analysis or breath testing are two methods that can accurately determine how much alcohol is present in the bloodstream. 

In general, some common signs of this level of intoxication include:

  • Disorientation, delayed reaction time, lack of coordination, or inability to walk
  • Depression
  • Rapid involuntary eye movement
  • Changes in speech volume
  • Red eyes
  • Mental confusion
  • Slurred speech
  • Amnesia
  • Bluish-colored or cold, clammy skin (sweating)
  • Trouble staying conscious
  • Hypothermia (lower than average body temperature)
  • Irregular heartbeat (arrhythmias) or breathing (10-second intervals or more between breaths)
  • Incontinence (inability to control bladder or bowel)
  • Seizures
  • Vomiting or choking
  • Unresponsiveness
  • Strong alcohol smell 

If you visit an emergency department, doctors may evaluate these signs plus other aspects, such as: 

  • A known history of chronic use
  • Possible use of another substance
  • The degree of impairment (slight, moderate, very, or extreme) 

When Should You Visit the Emergency Room (ER)?

If a person is suspected of alcohol poisoning, seek immediate medical help. They should not wait for symptoms to appear, as some people may not show symptoms or signs typically associated with a particular BAC. 

You should also avoid giving cold showers or hot coffee to a person experiencing alcohol poisoning. These actions could worsen the situation and cause more problems. 

A study published in the leading medical journal Alcohol and Alcoholism suggested that chronic drinkers may have built tolerance that would cover up visible signs of intoxication when BACs are over 100 mg/100 ml.

Treatment for Alcohol Abuse & Addiction

If you or a loved one has an alcohol use disorder (AUD), getting professional medical help is the first step on the path to recovery. Different therapeutic options are available, such as:

  • Cognitive-behavioral therapy (CBT)
  • Inpatient/outpatient treatment facilities
  • Support groups 
  • Medication-assisted treatment (MAT)

It is important not to quit drinking suddenly. Withdrawal symptoms can be severe and the risk of relapse and overdose increases. Treatment facilities provide medical supervision that can help you undergo a healthy, controlled detox and withdrawal process.

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Resources

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“Alcohol // Rev. James E. McDonald, C.S.C., Center for Student Well-Being // University of Notre Dame.” Rev. James E. McDonald, C.S.C., Center for Student Well-Being, 2020, mcwell.nd.edu/your-well-being/physical-well-being/alcohol/.

“Alcohol Poisoning: Symptoms, Treatment & Prevention.” Cleveland Clinic, 15 Oct. 2020, my.clevelandclinic.org/health/diseases/16640-alcohol-poisoning.

“Blood Alcohol Level: MedlinePlus Medical Test.” MedlinePlus, U.S. National Library of Medicine, 3 Dec. 2020, medlineplus.gov/lab-tests/blood-alcohol-level/

“Module 1: Gender Matters.” The Alcohol Pharmacology Education Partnership, Duke University, sites.duke.edu/apep/module-1-gender-matters/explore-more/summary-of-differences-between-girls-n-guys/.

Olson, Kalen N., et al. “Relationship Between Blood Alcohol Concentration and Observable Symptoms of Intoxication in Patients Presenting to an Emergency Department.” OUP Academic, Oxford University Press, 19 May 2013, academic.oup.com/alcalc/article/48/4/386/534528?searchresult=1.

“Understanding the Dangers of Alcohol Overdose.” National Institute on Alcohol Abuse and Alcoholism, U.S. Department of Health and Human Services, 1 Apr. 2020, www.niaaa.nih.gov/publications/brochures-and-fact-sheets/understanding-dangers-of-alcohol-overdose.

Zakhari, Samir. Overview: How Is Alcohol Metabolized by the Body?, National Institute on Alcohol Abuse and Alcoholism, pubs.niaaa.nih.gov/publications/arh294/245-255.pdf.

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