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Blood Alcohol Content

What is Blood Alcohol Content?

Blood Alcohol Content (BAC) is also called blood alcohol concentration and is the measurement of alcohol in the blood. It is expressed in mass/mass (mg/g or g/kg) or mass/volume(g/L or g/100 mL) units. The difference in units is extremely important for an accurate measure of alcohol in the bloodstream. Serum and plasma BAC concentrations are much different than whole blood.

What are Serum or Plasma Alcohol Concentrations?

Serum or plasma blood alcohol concentrations are the result of hospital clinical laboratory testing blood. This testing is done for health treatment purposes at the hospital. These results are not correct for the measurement of alcohol in a driver’s blood under the driving laws. Plasma contains around 92% water and will have a higher concentration of ethanol than whole blood by around 15%. Tests have shown that after drinking alcohol, ethanol blood alcohol in plasma was always higher than whole blood concentrations. Plasma testing has the same results as serum in terms of alcohol concentration.

What is the Blood Alcohol Level Legal Limit?

The United States blood alcohol legal limit for adults who are 21 years old or older is .08 in every state except Utah. Utah lowered the legal limit to .05 beginning December 31, 2018. A vocal critic of the new law is the American Beverage Institute. The claim that “Nearly 70 percent of alcohol-related fatalities in this country are caused by someone with a BAC of 0.15 and above.”

What are Blood Alcohol Level Effects?

BAC is many times measured as a percentage of the volume of alcohol in blood per units of blood(grams per 100mL). The range will be from .01 to possibly up to .5 or more, which could result in death.

Lethal Blood Alcohol Level

Studies from The National Institute of Health have shown that long-timee drinkers have a higher tolerance for alcohol and can have a higher BAC without dying. Someone with a low tolerance faces a higher risk of death at a level of .355, the mean level in 175 post mortem intoxication death cases.

Alcohol poisoning seems to be a discussion that occurs when there are concerns for college kids drinking large amounts of alcohol in a short amount of time. Sometimes it is a student’s death that causes the discussion to take place.

Overindulging with alcohol consumption in a short amount of time can result in obvious health dangers. Some problems that can put a person at risk of death include choking, stopping breathing, severe dehydration, seizures, hypothermia, irregular heartbeat, brain damage, and of course death by one of the listed causes.

Blood Alcohol Content Calculator

Everyone’s a little different when it comes to the effects of alcohol on the body. A blood alcohol calculator will just be guessing and will not be accurate. It is better to use a portable breathalyzer rather than something that uses a formula like the following:

BAC calculator Formula:
   BAC% = (A × 5.14/W × r) – .015 × H 

A=Alcohol consumed in ounces, W=body weight in pounds, r=Alcohol distribution ratio Men-.73 Women-.66, H=Time passed since drinking in hours.

What is Alcohol Rate of Absorption?

The speed of alcohol absorption is dependent on whether the drinker is eating or has eaten recently prior to drinking. Studies have shown that some alcohol disappears with the food during digestion. It was previously suggested by Widmark, in the 1930s, that some alcohol chemically bound to amino acids such as glycine preventing them from being absorbed into the bloodstream. Also, the composition of the food eaten affects ethanol absorption rates.

Alcohol Metabolism Rate

Alcohol absorbs through the gastrointestinal tract which includes the stomach. Alcohol can easily penetrate cell membranes. The organs with the most blood supply receive the alcohol first. This includes the brain and lungs. 

There are several factors that control the alcohol absorption rate. The strength of the alcohol beverage, food, sex, body weight, body water, many more. A renowned researcher Kurt Dubowski gave a single dose experiment in 1976. The peak blood alcohol times recorded ranged from 14 minutes to 138 minutes. The average time was 57 minutes for men and 42 minutes for women. 

Alcohol Elimination Rate

It was discovered in 1980 that an adequate protein diet was important in increasing the rate of ethanol elimination from the blood. This enhanced the liver blood flow and helped the clearance rate of ethanol from the blood.

Both absorption and elimination rates are greatly dependent on the food present. Elimination takes place through the urine, breath, perspiration as well as other means. The rate of elimination difference between men and women is not statistically significant. 

The proportion of fat to lean tissue will affect alcohol distribution in the body. Women do have less water per body mass unit so will have smaller volume distribution. Alcohol follows water entering the bloodstream, extracellular spaces, and intracellular spaces. Not in fat. A fatter person drinking the same volume will register a higher BAC compared to a skinny person weighing the same weight. 

A 155-pound person will eliminate about the same amount of alcohol as a some light beers, 7 grams per hour. 

Gender Difference in Alcohol Elimination

The gender difference in elimination greatly depends on water composition with the amount of water per pound of body weight. Women have less water per unit of body mass and so have a smaller distribution volume. A 2007 study by Dettling concluded that the elimination rate in women was slightly faster because their liver is a larger portion of a lean body mass than in males.

Can Medication Increase Blood Alcohol Levels?

No. Combined with drugs, alcohol levels do not increase but the effects of alcohol can increase. Ethanol reacts with a wide range of drugs. It can possibly have a synergistic effect when combined with drugs having a central nervous system depressant result.   

Cocaine and Alcohol

Cocaine and alcohol can be a dangerous combination and potentially damaging to the heart and liver. The combination creates euphoria enhancing metabolite called cocaethylene.  This has been proven to cause liver toxicity.

A very interesting result was found studying the combination of alcohol taken along with cocaine. Alcohol’s depressant properties are counteracted by cocaines central nervous system stimulant properties. Studies have shown that people dosed with alcohol and cocaine had reduced learning errors compared to a placebo. Errors in performance were also lower than when there was alcohol dosed alone. 

Alcohol and Marijuana

Marijuana contains tetrahydrocannabinol. This is the active component in marijuana metabolites. Alcohol has proven to affect psychomotor performance on driving skills. But a 1983 study found marijuana did not impair driving performance. A combination of both alcohol and marijuana showed a greater effect than with alcohol alone. 


There is no forensically accurate extrapolation in breath and blood alcohol concentration testing based on time and individual analysis results. Only with the relevant information can an expert witness even attempt to testify about the BAC curve at the time of driving. Such needed data would be the time of the first and last drink, alcohol content, food eaten, and whether BAC was increasing or decreasing after the driving.

“Extrapolation of a later alcohol test result to the time of the alleged offense is always of uncertain validity and therefore forensically unacceptable.” Kurt M. Dubowski Ph.D

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