Blood alcohol content (BAC)


Blood alcohol content (BAC), or blood alcohol concentration, is the concentration of alcohol in a person's blood. BAC can be mathematically estimated or measured with a blood, breath, or urine test. A blood alcohol level of 0.01 is considered low, while 0.4 and higher is toxic and potentially deadly.
When a person consumes alcohol it is absorbed into the bloodstream. Then the liver breaks down (metabolizes) the alcohol. Alcohol is metabolized more slowly than it is absorbed. Because it takes longer for alcohol to metabolized, consumption must be controlled in order to prevent alcohol from accumulating in the body and causing intoxication.
BAC is used to determine an individual's intoxication level, and it provides an estimate of his/her level of impairment. When individuals consume alcohol, their judgment, coordination, concentration, alertness, speech, and ability to feel sensations become impaired. The more an individual drinks, the more impaired these functions become.
Even though the degree of impairment varies among people with the same BAC, it is considered a reliable way to determine if it is safe for someone to drive or operate heavy machinery, including motor vehicles, boats, and aircrafts after drinking.
It is illegal for individuals to drive with BAC levels of 0.08 and higher in the United States. States may have stricter laws for individuals younger than 21 years old. Some states have zero tolerance laws for this age group that allow underage people to be convicted of driving under the influence with virtually any amount of alcohol in the bloodstream.
The amount of alcohol varies in different types of alcoholic drinks. In general, a 12-ounce beer, a five-ounce glass of wine, and 1.5-ounce shot of hard liquor are considered equivalent.
Counting the number of drinks consumed is not an accurate way to measure intoxication because individuals have different alcohol tolerances. An individual's tolerance to alcohol is dependent on many factors, including weight, age, gender, body fat percentage, genetics, synergistic effects of drugs, amount of food in the stomach, and how frequently the person drinks.
The length of time that elapses between drinks is also an important factor. The quicker an individual drinks alcoholic beverages, the more intoxicated he/she is going to become. This is because the body needs time to metabolize the alcohol. It is generally accepted that consuming two standard alcoholic beverages increases the average person's BAC by about 0.05% in about one hour. Limiting alcohol intake to one drink per hour after the first two drinks are consumed will keep the BAC near 0.05%.
Individuals should not consume any alcoholic beverages before driving or operating heavy machinery.

Related Terms

Alcohol, alcohol tolerance, alcoholic beverage, alcoholic drink, BAC, blood alcohol level, blood alcohol concentration, blood alcohol test, Breathalyzer® test, driving under the influence, drunk driving, DUI, intoxicated, intoxication, urine alcohol test.

alcohol and the body

Alcohol (also called ethanol) acts as a drug affecting the central nervous system (CNS). Its behavioral effects, such as slurred speech or stumbling, are a result of its influence on the response in the nervous tissue and not on the muscles or senses themselves. Alcohol is a depressant, and depending on the dose, it can be a mild tranquilizer or a general anesthetic.
At very low doses, alcohol can appear to be a stimulant by suppressing certain inhibitory brain functions. However, as the blood alcohol concentration increases, further suppression of nervous tissue functions produce the classic symptoms of intoxication, including slurred speech, unsteady gait, disturbed sensory perceptions, and inability to react quickly. At high concentrations, ethanol produces general anesthesia. A highly intoxicated person will be in a coma-like state and very difficult to wake. In extreme cases, if the alcohol concentration is high enough, it will inhibit basic involuntary bodily functions, such as breathing, and may cause death.
Alcohol is metabolized, or broken down, by the liver. Metabolism involves a number of processes, one of which is called as oxidation. Through oxidation in the liver, alcohol is detoxified. Alcohol and toxins are removed from the blood, preventing them from accumulating and destroying cells and organs. A small amount of alcohol escapes metabolism and is excreted unchanged in the breath, sweat, and urine. Until all the alcohol consumed has been metabolized, it is distributed throughout the body, affecting the brain and other tissues.
The liver can metabolize only a certain amount of alcohol per hour, regardless of the amount that has been consumed. The rate of alcohol metabolism depends, in part, on the amount of metabolizing enzymes in the liver, which varies among individuals. In general, after the consumption of one standard drink, the amount of alcohol in the drinker's blood peaks within 30-45 minutes. A standard drink is defined as 12 ounces of beer, five ounces of wine, or 1.5 ounces of 80-proof distilled spirits, all of which contain the same amount of alcohol. Alcohol is metabolized more slowly than it is absorbed. Therefore, consumption needs to be controlled in order to prevent alcohol from accumulating in the body and causing intoxication.
Some individuals may experience facial flushing in response to alcohol. Alcohol flush reaction occurs in individuals who have an inactive enzyme called aldehyde dehydrogenase 2 (ALDH2). This enzyme normally breaks down a byproduct of alcohol called acetaldehyde. Without ALDH2, acetaldehyde accumulates in the body and causes flushing. Other symptoms, such as dizziness, nausea, headache, and increased heartbeat, may also occur. Alcohol flush reaction is particularly common among Asian individuals. As many as 50% of Asians experience facial flushing in response to alcohol.