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Alcohol and the body
Calculations using blood alcohol curve
Using a blood alcohol curve it is possible to estimate the following:
- blood alcohol level at a given time based upon an indicated consumption scenario
- quantity of alcohol required to produce a known blood alcohol level at a given time
- blood alcohol concentration at a time previous to sample collection (retrograde extrapolation), or at a time subsequent to sample collection (anterograde extrapolation)
To accurately estimate each of the above, knowledge of certain factors is required. These may include:
- sex
- age
- height
- weight
- consumption start time and stop time
- pattern of drinking
- type of alcohol consumed including number of drinks, size and alcohol content
- time for which BAC is being calculated (or BAC value(s) detected if a retrograde or anterograde extrapolation is required)
- times meals eaten
- disease states
- any medications that were taken
This data combined with the empirical factors derived from scientific studies, such as average rates for alcohol absorption, distribution and elimination provides the basis for the estimates noted above.
To approximate your blood alcohol level at a particular point in time use the Calculator.
BAC Reporting Conventions
The Criminal Code of Canada reports the legal limit for alcohol as 80 milligrams of ethyl alcohol per 100 millilitres of blood (80 mg%). This is also often expressed as 0.08 grams of ethyl alcohol per 100 millilitres of blood.
In the clinical world, concentrations of substances are reported using the Systeme Internationale system of measurement. Hence, millimoles per litre. One millimole of ethyl alcohol per litre of blood is equivalent to 4.61 milligrams of ethyl alcohol per 100 millilitres of blood. As a result, 80 mg% is equivalent to 17.3 millimoles of ethyl alcohol per litre of blood.
Mg%: Milligrams of ethyl alcohol in 100 millilitres of blood.
Serum/Plasma versus Whole Blood
Hospital analysis of blood samples for ethyl alcohol content is often based upon serum or plasma as the sample matrix.
Plasma is the liquid portion of the circulating blood (whole blood).
Serum is the liquid remaining after the red blood cells are removed by some mechanical means, such as centrifugation. Serum contains slightly more water than whole blood and hence will have a slightly higher alcohol level than whole blood.
Scientific studies have shown that serum will contain more alcohol than whole blood by a factor of 1.08:1 to 1.18:1, or on average, 1.12:1. As a result, a serum alcohol level of 108-118 mg% would be equivalent to an alcohol level of 100 mg% in whole blood.