What Is Blood Alcohol Concentration

Blood Alcohol Concentration: Recognizing and Responding to Danger

A helpful way to understand BAC is to think of how a sponge holds water in much the same way as the body holds alcohol. The body is like a sponge that can absorb and hold a certain amount of liquid. The water you pour onto the sponge represents the alcohol you drink. When you pour water onto the sponge slowly, it absorbs the water more efficiently. This is like drinking alcohol slowly, allowing your body to metabolize or process it over time. 

If you pour water too quickly, the sponge becomes soaked and cannot absorb any more water, causing the excess to spill over. Similarly, if you drink alcohol too quickly, your body can’t process it fast enough, leading to an increase in BAC. The excess water spilling from the sponge represents the alcohol entering your bloodstream at a high rate.  This can lead to intoxication or being drunk and potentially alcohol poisoning.

How is BAC measured?

BAC (Blood Alcohol Concentration) is measured using several methods and tests. Here are the primary ways: 

• Breathalyzer Tests: Breathalyzers measure the amount of alcohol in a person’s breath. They estimate BAC by analyzing the alcohol content in a breath sample, which is linked to the alcohol concentration in the blood. 

• Blood Tests: A blood test directly measures the amount of alcohol present in a person’s blood. A sample of blood is taken and analyzed in a lab. It is considered the most accurate method for determining BAC. It is often used in legal and medical settings. 

• Urine Tests: Urine tests estimate BAC by measuring the amount of alcohol in urine. However, alcohol can be detected in urine for a longer period after consumption, making it less accurate for current BAC levels. 

• Saliva Tests: Saliva tests measure the amount of alcohol present in a saliva sample. The results can estimate BAC based on the concentration of alcohol in the saliva. 

Blood tests are the most accurate, while breathalyzers are portable and provide immediate results with a good degree of accuracy. Urine and saliva tests are less precise and less commonly used for immediate BAC measurement.

How can a person figure out their BAC?

The easiest ways to calculate BAC are to use an online calculator or a mobile app. It’s important to note that these methods provide an estimate and may not be accurate.  

There are several factors that can influence BAC. They include the amount of alcohol one drinks, how quickly, body weight, sex, and metabolism.  

Older adults generally process alcohol more slowly than younger individuals, which can result in higher BAC levels for the same amount of alcohol consumed. Also, they tend to have less body water. Since alcohol is water-soluble (e.g., dissolves in water), lower body water content can lead to higher BAC.

Several medications interact with alcohol, potentially affecting BAC and alcohol’s effects.¹ Among them are antibiotics, antidepressants, sleep medications, antihistamines, pain medications and anti-anxiety medications. This can have serious and potentially fatal effects. Be sure to speak to your prescriber to understand how these medications affect your BAC. 

Biological sex makes a difference too. People assigned female at birth generally have a higher amount of body fat and less body water compared to people assigned male at birth. Since alcohol is less soluble (less able to dissolve) in fat and more soluble in water, this difference can result in higher BAC levels in women than men even if they consume the same amount of alcohol. 

People assigned female at birth typically have lower levels of the enzyme alcohol dehydrogenase, which is responsible for breaking down alcohol in the stomach. This can result in more alcohol entering the bloodstream, leading to higher BAC. Additionally, hormonal changes, especially those related to the menstrual cycle, can affect how alcohol is processed in women.

How long does it take for BAC to return to zero?

The time it takes for BAC to return to zero depends on several factors, including the amount of alcohol consumed, body weight, metabolism and overall health. On average, the body metabolizes alcohol at a rate of about 0.015% BAC per hour. This means if your BAC is 0.08%, it would take approximately 5 to 6 hours for it to drop to zero.²

If you have consumed alcohol and are unsure about your BAC, using a breathalyzer or seeking professional testing can provide a more accurate assessment.

What are the signs of a high BAC?

Here are common signs associated with different levels of high BACs: ³

 BAC 0.08% – 0.15% (note, .08% is the legal limit for driving in most states). 

• Difficulty with balance and motor skills, such as stumbling or clumsiness.  

• Poor decision-making, increased risk-taking, and trouble assessing consequences. 

• Slurred speech that may not make sense. 

• Feeling sleepy or having no energy 

BAC 0.16% – 0.30% 

• Significant difficulty with motor skills and coordination; struggling to walk or perform basic tasks. 

• Difficulty understanding or processing information; disorientation. 

• Increased likelihood of nausea and vomiting. 

• Extreme mood swings, such as sudden anger or euphoria. 

• Blurred vision. 

BAC 0.31% – 0.40% 

• Semi-conscious or semi-alert state; difficulty responding to stimuli. 

• Unresponsiveness: difficulty waking up or responding 

• Problems breathing 

• Risk of passing out or unconscious 

BAC Above 0.40% 

• High risk of severe alcohol poisoning, which can lead to coma or death. 

• Complete unconsciousness 

• Dangerously low body temperature due to alcohol’s effects on the body. 

• Risk of death  

Additional symptoms for all high BAC levels include poor memory or difficulty remembering events or experiencing blackouts. A person may have trouble walking or standing without support. It can be hard to form logical thoughts and sentences. Additionally, a person may be unable perform simple tasks or operate machinery, including a car.

What is alcohol poisoning?

Alcohol poisoning is a serious and potentially deadly consequence of drinking large amounts of alcohol in a short period. It occurs when there is so much alcohol in the bloodstream that areas of the brain controlling basic life-support functions—such as breathing, heart rate, and temperature control—begin to shut down. 

Signs of alcohol poisoning include confusion, vomiting, seizures, breathing problems, low body temperature, blue-tinged or pale skin, and/or if the person has passed out.

Do’s and don’ts if you suspect alcohol poisoning

Do’s 

1. Call 911 or your local emergency number immediately. 
2. Keep the person awake and sitting up if possible. 
3. If the person is unconscious, place them on their side in the recovery position to prevent choking on vomit. 
4. Stay with the person and monitor their symptoms until help arrives. 
5. Provide information to emergency responders, such as how much alcohol the person consumed, over what period, and any other substances they may have taken. 

Don’ts

1. Do not leave the person alone, even if they appear to be sleeping. 
2. Do not try to make the person vomit, as this can lead to choking. 
3. Do not give the person coffee, caffeine, or other stimulants, as these do not reverse the effects of alcohol poisoning. 
4. Do not put the person in a cold shower, as this can cause a drop in body temperature and lead to hypothermia. 
5. Do not try to walk the person around, as this does not help sober them up and can increase the risk of falls and injuries.

In cases of suspected alcohol poisoning, it’s important to get medical attention immediately to prevent severe complications and potential death.

Will a breathalyzer help?

If you’re worried about a loved one’s drinking, using a breathalyzer can help you see how much alcohol is in their system, which might be useful in some situations. A breathalyzer gives you a measure of their BAC and can provide immediate feedback, helping you know if they’re too drunk to do things like drive. It can also help them understand how much they’ve had to drink.  

On the other hand, using a breathalyzer can also be tricky. It might make your loved one feel like you don’t trust them, which could hurt your relationship. Some loved ones will offer to take a breathalyzer and then drink afterwards, or they will argue that they aren’t drunk.  Plus, it doesn’t address the underlying reasons why they might be drinking too much. If you’re concerned, you may want to talk to a counselor or other healthcare provider, who can offer more help.

Start by having a calm and caring conversation with your loved one about your worries. Let them know you care and want to support them. Encourage them to see a professional if needed and provide them with tools to drink more safely. Learn about alcohol use disorder and the help available for people dealing with it. Lastly, set clear boundaries about alcohol use and its effects on your relationship. If you need help developing a plan or want to talk it over with one of our helpline specialists, please reach out.