Blood Alcohol Concentration (BAC) & Associated Clinical Signs Expert Overview

In this document, toxicologist Dr. Michael Whitekus provides a comprehensive reference table outlining a spectrum of Blood Alcohol Concentration (BAC) levels. His analysis includes the number of drinks consumed to attain specific BACs and prominent clinical signs corresponding with specific BAC ranges. Dr. Whitekus’ reference also demonstrates how the relative risk of being involved in a motor vehicle crash increases exponentially with heightened BAC levels.

Clinical Signs Associated With Blood Alcohol Concentration (BAC)

Blood alcohol concentration (BAC) and alcohol consumption can be estimated based on scientifically valid standard methodology used by toxicologists [1] and this information can be used to answer key questions in alcohol related cases like the following;

1. How many drinks did the individual consume?
2. What was their BAC and prominent clinical signs at the time of the last drink served and/or the crash incident?

This methodology relies on i) the principles of alcohol pharmacokinetics, ii) the gender, age, height and weight of the drinking individual, iii) the time period that they were reportedly consuming alcoholic beverages, and iv) the measured BAC and time of blood draw (if data are available) (1).

In Table 1 below the number of drinks a typical male or female would need to consume to generate the identified BAC, and the list of clinical signs that would be expected from the BAC range are listed along with the relative risk of being in a fatal car crash while driving at the identified BAC.

Interesting Facts Related to the Blood Alcohol Table (Table 1)

• The number of drinks that a typical woman^b needs to consume to generate a given BAC is less than a typical man^a for two reasons, i) women typically weigh less than men and ii) a woman’s body (of equal height and weight) contains more fat than a man’s body which reduces her ability to absorb alcohol (volume of distribution is reduced).
• Driving Impairment begins at a BAC of ~0.02 % (~2 standard drinks for a male^a and ~1 standard drink for a female^b).
• A drinker’s ability to drive safely is negatively impacted prior to their ability to detect any outward changes in their behavior or driving ability.
• An individual who chooses to drive at a BAC of 0.08 % (the legal limit, ~4 standard drinks for a male^a and ~3 standard drinks for a female^b) is ~10 times more likely to be involved in a car crash than a sober driver.
• An individual who is visibly intoxicated (BAC of ~0.15 % or greater) and allowed to drive is 78 times more likely to be involved in a car crash.
• The pleasurable and most socially desirable effects of alcohol are typically attained at BACs of 0.03-0.12 % or approximately 2-6 drinks for a male^a and 1-4 drinks for a female^b.
• Once a social drinker is visibly intoxicated (BAC of ~0.15%, ~7 drinks for a male^a and ~4-5 drinks for a female^b as depicted in Table 1) there are no socially desirable effects associated with further drinking.

a. Based on a 5’10’’, 25 year old, 175 lb male.
b. Based on 5’4’’, 25 year old, 125 lb female.
c. Empty stomach, drinking alcohol for 60 minutes followed by 30 minutes of non-drinking activity. One standard drink equals 14 g of alcohol or 5 oz wine (12%), 12 oz beer (5%), 1.5 oz liquor (40%). Assuming an elimination rate of 18 mg/dL/h.
d. The relative risk (x times greater) of being in a fatal single motor vehicle crash compared to driving sober. Data are for male/female, age 21-34.
ND= No data

References:

1. Brick, J., Standardization of alcohol calculations in research. Alcohol Clin Exp Res, 2006. 30(8): p. 1276-87.
2. Moskowitz, H., and C. Robinson, Effects of Low Doses of Alcohol on Driving-related Skills: A Review of the Evidence, National Highway Traffic and Safety Administration, Editor. 1988.
3. Brick, J. and C.K. Erickson, Intoxication is not always visible: an unrecognized prevention challenge. Alcohol Clin Exp Res, 2009. 33(9): p. 1489-507.
4. Caplan, Y.H., B.A. Goldberger, Garriott’s Medicolegal Aspects of Alcohol. 6th ed. 2015, Tucson, Arizona: Lawyers and Judges Publishing Company, Inc.
5. Moskowitz, H., Burns, M., Fiorentino, D., Smiley, A., and Zador, P., Driver Characteristics and Impairment at Various BACs, NHTSA, Editor. 2000.
6. Moskowitz, H. and M. Burns, Effects of rate of drinking on human performance. J Stud Alcohol, 1976. 37(5): p. 598-605.
7. National Academies of Sciences, Engineering, and Medicine. 2018. Getting to Zero Alcohol-Impaired Driving Fatalities: A Comprehensive Approach to a Persistent Problem. Washington, DC: The National Academies Press. https://doi.org/10.17226/24951.

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Featured Expert

Michael J. Whitekus, Ph.D., DABT

Toxicology & Drug Safety Expert

Dr. Michael Whitekus is a board certified toxicologist, with advanced degrees in chemistry and toxicology, and over 25 years of academic and industry experience. He has extensive expertise evaluating… read more.