Blood alcohol content explained

Blood alcohol content
Synonyms:Blood alcohol concentration, blood ethanol concentration, blood alcohol level, blood alcohol
Loinc:,,,

Blood alcohol content (BAC), also called blood alcohol concentration or blood alcohol level, is a measurement of alcohol intoxication used for legal or medical purposes.[1]

BAC is expressed as mass of alcohol per volume of blood. In the US and many international publications, BAC levels are written as a percentage such as 0.08%, meaning that there is 0.08 g of alcohol for every 100 of blood. In different countries, the maximum permitted BAC when driving ranges from the limit of detection (zero tolerance) to 0.08%.[2] [3] BAC levels above 0.40% are potentially fatal.

Units of measurement

BAC is generally defined as a fraction of weight of alcohol per volume of blood, with an SI coherent derived unit of kg/m3 or equivalently grams per liter (g/L). Countries differ in how this quantity is normally expressed. Common formats are listed in the table below. For example, the US and many international publications present BAC as a percentage, such as 0.05%. This would be interpreted as 0.05 grams per deciliter of blood. This same concentration could be expressed as 0.5‰ or 50 mg% in other countries.[4]

Sign Units Used in
1 percent (%), 1 g% = = = 1 g/100 mL US, Australia,[5] Canada[6]
1 per mille (‰) = = 100 mg/1 dL Austria, Belgium, Bulgaria, Czech Republic, Denmark, France, Germany, Latvia, Lithuania, Netherlands, Poland,[7] Portugal, Romania, Russia, Slovenia, Spain, Sweden, Switzerland, Turkey
= = 1 mg/100 mL United Kingdom[8] Ireland, Canada, New Zealand

It is also possible to use other units. For example, in the 1930s Widmark measured alcohol and blood by mass, and thus reported his concentrations in units of g/kg or mg/g, weight alcohol per weight blood. 1 mL of blood has a mass of approximately 1.055 grams, thus a mass-volume BAC of 1 g/L corresponds to a mass-mass BAC of 0.948 mg/g. Sweden, Denmark, Norway, Finland, Germany, and Switzerland use mass-mass concentrations in their laws, but this distinction is often skipped over in public materials,[9] implicitly assuming that 1 L of blood weighs 1 kg.[10]

In pharmacokinetics, it is common to use the amount of substance, in moles, to quantify the dose. As the molar mass of ethanol is 46.07 g/mol, a BAC of 1 g/L is 21.706 mmol/L (21.706 mM).[11]

Effects by alcohol level

Alcohol levelEffectsRef
BACper millemg%
0.01–0.05%0.1–0.510–50Mild relaxation and reduced social inhibition; impaired judgment and coordination
0.06–0.20%0.6–260–200Emotional swings, impaired vision, hearing, speech, and motor skills
0.2–0.3%2–3200–300Urinary incontinence, vomiting, and symptoms of alcohol intoxication
0.3–0.4%3–4300–400Potential total loss of consciousness; signs of severe alcohol intoxication
>0.4%>4>400Potentially fatal, may result in a coma or respiratory failure
The magnitude of sensory impairment may vary in people of differing weights.[12] The NIAAA defines the term "binge drinking" as a pattern of drinking that brings a person's blood alcohol concentration (BAC) to 0.08 grams percent or above.[13]

Estimation

Direct measurement

Blood samples for BAC analysis are typically obtained by taking a venous blood sample from the arm. A variety of methods exist for determining blood-alcohol concentration in a blood sample.[14] Forensic laboratories typically use headspace-gas chromatography combined with mass spectrometry or flame ionization detection,[15] as this method is accurate and efficient.[14] Hospitals typically use enzyme multiplied immunoassay, which measures the co-enzyme NADH. This method is more subject to error but may be performed rapidly in parallel with other blood sample measurements.[16]

In Germany, BAC is determined by measuring the serum level and then converting to whole blood by dividing by the factor 1.236. This calculation underestimates BAC by 4% to 10% compared to other methods.[17]

By breathalyzer

See main article: Breathalyzer. The amount of alcohol on the breath can be measured, without requiring drawing blood, by blowing into a breathalyzer, resulting in a breath alcohol content (BrAC). The BrAC specifically correlates with the concentration of alcohol in arterial blood, satisfying the equation . Its correlation with the standard BAC found by drawing venous blood is less strong.[18] Jurisdictions vary in the statutory conversion factor from BrAC to BAC, from 2000 to 2400. Many factors may affect the accuracy of a breathalyzer test,[19] but they are the most common method for measuring alcohol concentrations in most jurisdictions.[20]

By intake

Blood alcohol content can be quickly estimated by a model developed by Swedish professor Erik Widmark in the 1920s.[21] The model corresponds to a pharmacokinetic single-compartment model with instantaneous absorption and zero-order kinetics for elimination. The model is most accurate when used to estimate BAC a few hours after drinking a single dose of alcohol in a fasted state, and can be within 20% CV of the true value.[22] [23] It is not at all realistic for the absorption phase, and is not accurate for BAC levels below 0.2 g/L (alcohol is not eliminated as quickly as predicted) and consumption with food (overestimating the peak BAC and time to return to zero).[24] [25] The equation varies depending on the units and approximations used, but in its simplest form is given by:[26]

EBAC=

A
Vd

-\beta x T

where:

Examples:

EBAC = 28/(0.71 \cdot 80) - (0.148 \cdot 2) \approx 0.197 \text = 0.0197% \text

EBAC = 21/(0.58 \cdot 70) - (0.156 \cdot 2) \approx 0.205 \text = 0.0205% \text

In terms of fluid ounces of alcohol consumed and weight in pounds, Widmark's formula can be simply approximated as[21]

EBAC=8 x floz/weightinpounds-\beta x T

for a man or

EBAC=10 x floz/weightinpounds-\beta x T

for a woman, where EBAC and factors are given as g/dL (% BAC), such as a factor of 0.015% BAC per hour.[21]

By standard drinks

See main article: Standard drink. The examples above define a standard drink as 0.6 fluid ounces (14 g or 17.7 mL) of ethanol, whereas other definitions exist, for example 10 grams of ethanol.

Approximate blood alcohol percentage (by volume)[31]
Based on one drink having 0.5USoz alcohol by volume
DrinksSexBody weight
40 kg
90 lb		45 kg
100 lb		55 kg
120 lb		64 kg
140 lb		73 kg
160 lb		82 kg
180 lb		91 kg
200 lb		100 kg
220 lb		109 kg
240 lb
1 Male – 0.04 0.03 0.03 0.02 0.02 0.02 0.02 0.02
Female 0.05 0.05 0.04 0.03 0.03 0.03 0.02 0.02 0.02
2 Male – 0.08 0.06 0.05 0.05 0.04 0.04 0.03 0.03
Female 0.10 0.09 0.08 0.07 0.06 0.05 0.05 0.04 0.04
3 Male – 0.11 0.09 0.08 0.07 0.06 0.06 0.05 0.05
Female 0.15 0.14 0.11 0.10 0.09 0.08 0.07 0.06 0.06
4 Male – 0.15 0.12 0.11 0.09 0.08 0.08 0.07 0.06
Female 0.20 0.18 0.15 0.13 0.11 0.10 0.09 0.08 0.08
5 Male – 0.19 0.16 0.13 0.12 0.11 0.09 0.09 0.08
Female 0.25 0.23 0.19 0.16 0.14 0.13 0.11 0.10 0.09
6 Male – 0.23 0.19 0.16 0.14 0.13 0.11 0.10 0.09
Female 0.30 0.27 0.23 0.19 0.17 0.15 0.14 0.12 0.11
7 Male – 0.26 0.22 0.19 0.16 0.15 0.13 0.12 0.11
Female 0.35 0.32 0.27 0.23 0.20 0.18 0.16 0.14 0.13
8 Male – 0.30 0.25 0.21 0.19 0.17 0.15 0.14 0.13
Female 0.40 0.36 0.30 0.26 0.23 0.20 0.18 0.17 0.15
9 Male – 0.34 0.28 0.24 0.21 0.19 0.17 0.15 0.14
Female 0.45 0.41 0.34 0.29 0.26 0.23 0.20 0.19 0.17
10 Male – 0.38 0.31 0.27 0.23 0.21 0.19 0.17 0.16
Female 0.51 0.45 0.38 0.32 0.28 0.25 0.23 0.21 0.19
Subtract approximately 0.01 every 40 minutes after drinking.

By training

If individuals are asked to estimate their BAC, then given accurate feedback via a breathalyzer, and this procedure is repeated a number of times during a drinking session, studies show that these individuals can learn to discriminate their BAC, to within a mean error of 9 mg/100 mL (0.009% BAC).[32] The ability is robust to different types of alcohol, different drink quantities, and drinks with unknown levels of alcohol. Trained individuals can even drink alcoholic drinks so as to adjust or maintain their BAC at a desired level.[33] Training the ability does not appear to require any information or procedure besides breathalyzer feedback, although most studies have provided information such as intoxication symptoms at different BAC levels. Subjects continue to retain the ability one month after training.[34]

Post-mortem

After fatal accidents, it is common to check the blood alcohol levels of involved persons. However, soon after death, the body begins to putrefy, a biological process which produces ethanol. This can make it difficult to conclusively determine the blood alcohol content in autopsies, particularly in bodies recovered from water.[35] [36] [37] [38] For instance, following the 1975 Moorgate tube crash, the driver's kidneys had a blood alcohol concentration of 80 mg/100 mL, but it could not be established how much of this could be attributed to natural decomposition.[39] Newer research has shown that vitreous (eye) fluid provides an accurate estimate of blood alcohol concentration that is less subject to the effects of decomposition or contamination.[40]

Legal limits

See main article: Drunk driving law by country.

For purposes of law enforcement, blood alcohol content is used to define intoxication and provides a rough measure of impairment. Although the degree of impairment may vary among individuals with the same blood alcohol content, it can be measured objectively and is therefore legally useful and difficult to contest in court. Most countries forbid operation of motor vehicles and heavy machinery above prescribed levels of blood alcohol content. Operation of boats and aircraft is also regulated. Some jurisdictions also regulate bicycling under the influence. The alcohol level at which a person is considered legally impaired to drive varies by country.

Test assumptions

Extrapolation

Retrograde extrapolation is the mathematical process by which someone's blood alcohol concentration at the time of driving is estimated by projecting backwards from a later chemical test. This involves estimating the absorption and elimination of alcohol in the interim between driving and testing. The rate of elimination in the average person is commonly estimated at 0.015 to 0.020 grams per deciliter per hour (g/dL/h),[41] although again this can vary from person to person and in a given person from one moment to another. Metabolism can be affected by numerous factors, including such things as body temperature, the type of alcoholic beverage consumed, and the amount and type of food consumed.

In an increasing number of states, laws have been enacted to facilitate this speculative task: the blood alcohol content at the time of driving is legally presumed to be the same as when later tested. There are usually time limits put on this presumption, commonly two or three hours, and the defendant is permitted to offer evidence to rebut this presumption.

Forward extrapolation can also be attempted. If the amount of alcohol consumed is known, along with such variables as the weight and sex of the subject and period and rate of consumption, the blood alcohol level can be estimated by extrapolating forward. Although subject to the same infirmities as retrograde extrapolation—guessing based upon averages and unknown variables—this can be relevant in estimating BAC when driving and/or corroborating or contradicting the results of a later chemical test.

Metabolism

The pharmacokinetics of ethanol are well characterized by the ADME acronym (absorption, distribution, metabolism, excretion). Besides the dose ingested, factors such as the person's total body water, speed of drinking, the drink's nutritional content, and the contents of the stomach all influence the profile of blood alcohol content (BAC) over time. Breath alcohol content (BrAC) and BAC have similar profile shapes, so most forensic pharmacokinetic calculations can be done with either. Relatively few studies directly compare BrAC and BAC within subjects and characterize the difference in pharmacokinetic parameters. Comparing arterial and venous BAC, arterial BAC is higher during the absorption phase and lower in the postabsorptive declining phase.[42]

Highest levels

See also: List of deaths through alcohol.

There have been reported cases of blood alcohol content higher than 1%:

References

General and cited references

External links

Notes and References

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  2. News: Drink-drivers in Nepal face the 'smell test' crackdown . Yahoo News . 22 July 2012 . en-SG.
  3. Web site: Legal BAC limits by country. World Health Organization. 12 November 2023. none.
  4. Web site: http://www.mecinca.net/ALCOHOLIMETROS_Alcosim/BAC%20BrAC%20conversion%20table[1.pdf BAC Formats ]. 3 November 2023.
  5. Web site: 8 February 2022 . Original date 14 February 2017 . Blood alcohol levels . Alcohol and Drug Foundation (Australia).
  6. Web site: n.d. . Blood Alcohol Concentration (BAC) . 21 July 2022 . Mothers Against Drunk Driving (MADD Canada).
  7. 2019-10-15 . Nietrzeźwość a ryzyko zgonu w wypadku komunikacyjnym = Insobriety and the risk of death in traffic accident Journal of Education, Health and Sport . Journal of Education, Health and Sport . pl.
  8. Web site: The drink drive limit . 3 November 2023 . GOV.UK . en.
  9. Web site: Drink-driving: What are the rules? . www.ch.ch . en.
  10. News: Nager . Anna . Alkoholpromille, beräkning. Calculation of alcohol per mille . 13 April 2024 . Netdoktor . 4 May 2020 . sv-SE. I detta sammanhang räknar man med att 1 liter blod väger 1 kilo.. In this context, it is assumed that 1 liter of blood weighs 1 kilogram..
  11. Web site: Ethanol . 3 November 2023 . pubchem.ncbi.nlm.nih.gov . en.
  12. Dunn . Richard A. . Tefft . Nathan W. . 2014 . Has Increased Body Weight Made Driving Safer? . Health Economics . en . 23 . 11 . 1374–1389 . 10.1002/hec.2991 . 4135023 . 24038409.
  13. "Quick Stats: Binge Drinking." The Centers for Disease Control and Prevention. April 2008.https://www.cdc.gov/alcohol/quickstats/binge_drinking.htm.
  14. Dubowski . Kurt M. . Alcohol Determination in the Clinical Laboratory . American Journal of Clinical Pathology . 1 November 1980 . 74 . 5 . 747–750 . 10.1093/ajcp/74.5.747 . 7446484 .
  15. Zamengo . Luca . Tedeschi . Gianpaola . Frison . Giampietro . Griffoni . Carlo . Ponzin . Diego . Jones . Alan Wayne . Inter-laboratory proficiency results of blood alcohol determinations at clinical and forensic laboratories in Italy . Forensic Science International . 1 February 2019 . 295 . 213–218 . 10.1016/j.forsciint.2018.12.018 . 30611561 . 58591654 . 0379-0738.
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  17. Jones . Alan Wayne . Concentration units used to report blood‐ and breath‐alcohol concentration for legal purposes differ between countries which is important to consider when blood/breath ratios of alcohol are compared and contrasted . Journal of Forensic Sciences . 22 March 2024 . 10.1111/1556-4029.15511.
  18. Lindberg . L. . Brauer . S. . Wollmer . P. . Goldberg . L. . Jones . A.W. . Olsson . S.G. . Breath alcohol concentration determined with a new analyzer using free exhalation predicts almost precisely the arterial blood alcohol concentration . Forensic Science International . May 2007 . 168 . 2–3 . 200–207 . 10.1016/j.forsciint.2006.07.018. 16978819 .
  19. Jones . AW . Cowan . JM . Reflections on variability in the blood-breath ratio of ethanol and its importance when evidential breath-alcohol instruments are used in law enforcement. . Forensic Sciences Research . 3 August 2020 . 5 . 4 . 300–308 . 10.1080/20961790.2020.1780720 . 33457048. 7782040 . free .
  20. Williams . Paul M. . Current defence strategies in some contested drink-drive prosecutions: Is it now time for some additional statutory assumptions? . Forensic Science International . 1 December 2018 . 293 . e5–e9 . 10.1016/j.forsciint.2018.09.030. 30342920 . free .
  21. Web site: Ed Kuwatch . Fast Eddie's 8/10 Method of Hand Calculating Blood Alcohol Concentration: A Simple Method For Using Widmark's Formula . https://web.archive.org/web/20031202155933/http://www.dui-law.com/810art.htm . 2003-12-02 .
  22. Zuba . Dariusz . Piekoszewski . Wojciech . Uncertainty in Theoretical Calculations of Alcohol Concentration . Proc. 17th Internat. Conf. on Alcohol, Drugs and Traffic Safety . 2004 .
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  24. Searle . John . Alcohol calculations and their uncertainty . Medicine, Science and the Law . January 2015 . 55 . 1 . 58–64 . 10.1177/0025802414524385 . 24644224. 4361698 .
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  26. Maskell . Peter D. . Jones . A. Wayne . Heymsfield . Steven B. . Shapses . Sue . Johnston . Atholl . Total body water is the preferred method to use in forensic blood-alcohol calculations rather than ethanol's volume of distribution . Forensic Science International . November 2020 . 316 . 110532 . 10.1016/j.forsciint.2020.110532. 33099270 . 224966411 .
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  30. Maskell . Peter D. . Jones . A. Wayne . Heymsfield . Steven B. . Shapses . Sue . Johnston . Atholl . Total body water is the preferred method to use in forensic blood-alcohol calculations rather than ethanol's volume of distribution . Forensic Science International . November 2020 . 316 . 110532 . 10.1016/j.forsciint.2020.110532. 33099270 . 224966411 .
  31. http://www.alcohol.vt.edu/Students/alcoholEffects/estimatingBAC/index.htm BAC Charts
  32. Huber . H . Karlin . R . Nathan . P E . Blood alcohol level discrimination by nonalcoholics. The role of internal and external cues. . Journal of Studies on Alcohol . January 1976 . 37 . 1 . 27–39 . 10.15288/jsa.1976.37.27. 2811 .
  33. Rowan . D. C. . The Role of Blood Alcohol Level Estimation in Training Alcoholics to become Controlled Drinkers . British Journal of Addiction to Alcohol & Other Drugs . March 1978 . 73 . 3 . 316–318 . 10.1111/j.1360-0443.1978.tb00159.x. 280356 .
  34. Kelly . Alexandra R. . Fillmore . Mark T. . Use of mindfulness training to improve BAC self-estimation during a drinking episode. . Psychology of Addictive Behaviors . 24 August 2023 . 10.1037/adb0000955. 37616096 . 10907993 . February 24, 2025 . 261098937 .
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  38. Best-practices approach to determination of blood alcohol concentration (BAC) at specific time points: Combination of ante-mortem alcohol pharmacokinetic modeling and post-mortem alcohol generation and transport considerations. 10.1016/j.yrtph.2016.03.020. 2016. Cowan. Dallas M.. Maskrey. Joshua R.. Fung. Ernest S.. Woods. Tyler A.. Stabryla. Lisa M.. Scott. Paul K.. Finley. Brent L.. Regulatory Toxicology and Pharmacology. 78. 24–36. 27041394.
  39. News: Moorgate Alcohol Finding. The Guardian. 16 April 1975. 24.
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  48. Web site: Łuba. Marcin. Śmiertelny rekord: Kierowca z powiatu ostrołęckiego miał 22 promile alkoholu! Zginął w wypadku. eOstroleka.pl. 2017-11-04. pl. 24 October 2012.
  49. Web site: Miał 13,74 promila alkoholu we krwi. I przeżył. Rekord świata? . He had 13.74 blood alcohol levels. And he survived. World record? . 2013-08-08 . dead . https://web.archive.org/web/20130811065906/http://wiadomosci.gazeta.pl/wiadomosci/1%2C114871%2C14402847%2CMial_13_74_promila_alkoholu_we_krwi__I_przezyl__Rekord.html . 2013-08-11 .
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