Alcohol; Absorption, Effects, Metabolism & Testing

Introduction of Alcohol to the Bloodstream

absorption_01.gif (24258 bytes)When a person drinks alcohol the introduction into the blood will begin in very short order. It is facilitated when it comes in contact with mucous membranes such as the lining of the stomach (20-25%) and upper sections of the small intestine (70-75%) and to a lesser extend the mid and lower sections, where it passes through to the blood and is dissolved to be transported throughout the body. On an empty stomach a significant amount of the alcohol consumed will enter the bloodstream in just a few minutes, otherwise several minutes and can be as long as a few hours. Since it takes about a minute for the blood to completely circulate the effect on the brain is very quick resulting in all the symptoms "we all know".
Remember that all alcohol consumed must pass though the bloodstream regardless of the rate of absorption.

How Much and the Effect

drinking_01.jpg (20790 bytes)How much it affects depends on several factors, but the absolute dominant factor is a person's weight (total volume). A person weighing 100kg can generally drink twice as much as a person weighing 50kg and each will reach the same Blood Alcohol Concentration (BAC).
Think of it as having 2 glasses of water. One being 100ml and the other 50ml and both are 80% full and then calculate how much alcohol you can pour in the bigger glass before each overflow. The answer is twice as much. To a small extend body fat and individual metabolism also play a role. The answer is that there is no one accurate answer as to the amount one can consume, though some guessing using tables available on the Internet may serve as a guide.

The effect that alcohol has on an individual is relative to BAC differs from person to person. BAC is an absolute value and the one and only used in enforcement to determine the level of intoxication. Some people can handle themselves better than others when inebriated (holding ones alcohol) where others seem to be greatly affected after a relative small consumption of alcohol.
Whatever the individual effect that the alcohol has, it is worth noting that one of the soonest body impairment when coming under the influence is ones own judgment.

liver_01.jpg (27361 bytes)Metabolizing Alcohol

About 95% of all alcohol consumed has to be metabolized by the liver. The remaining 5% is excreted through urine, perspiration and breath. In a two stage process the liver uses enzymes to process ethanol. First it is transformed into acetaldehyde which is a toxic carcinogen, but quickly broken down to into less toxic acetate. Other tissues in the body further break down the acetate into CO2 and H2O.
The most important thing to note about the liver is that it works in a near fixed rate regardless of other factors. The rate is 0.016% BAC per hour, unless the liver is damaged in which case the rate is slower. This rate is largely irrespective of weight and gender.

Affecting the Rate of Alcohol Absorption

As mentioned earlier drinking on an empty stomach can cause an absorption rate that is faster than after a meal. Depending on individual desires and goals it is possible to affect the rate by certain means.
Using carbonated soft drinks or drinks high in electrolyte (such as Gatorade) as mixers will cause a faster rate of absorption.
Drinks with a high concentration of alcohol will be absorbed faster a drink with a lower concentration even if the total amount of alcohol consumed is the same.
Drinking while or shortly after consuming a fatty and high protein meal can greatly slow the absorption rate.

Respiratory System & Alcohol in Breath

lungs_01.gif (54138 bytes)The normal breathing cycle consists of inhaling fresh air containing a sufficient concentration of oxygen that when entering the lungs will come in contact with pulmonary alveolus linings. Alveoli are small hollow cavities with thin porous walls separating the gas chamber from the blood vessels in the lungs facilitating gas exchanges. These exchanges are oxygen being absorbed in to the bloodstream and the waste product, CO2, being released and subsequently exhaled.

A similar gas exchange takes place during the breathing cycle where alcohol vapors are released from the blood into the gas chamber of the lungs and exhaled.
The amount of alcohol that is released from the blood and in to the lung is very small relative to the actual concentration in the blood, hence is has no material effect in the reduction of blood alcohol concentration, but the amount is large enough to create a concentration in the exhalation that it is measurable with sensitive detectors.
That concentration is well defined. In other words if the concentration alcohol vapors in the exhaled air can be accurately measured the actual blood BAC in the blood can be determined by a multiplication factor.

What is BAC

BAC is an abbreviation of Blood Alcohol Concentration and is a measure for how much alcohol there is in the blood relative to the volume of blood. Not how much alcohol has been consumed.
Depending on country the unit of measure may differ with the two most common being percent (%) and promille (). Promille may be expressed in g/L or g/Kg (1.06 correction factor). The ratio between % and is 1:10 meaning 0.05% equals 0.5 (g/L).
The legal limits for operating a motor vehicle varies between countries, often between 0.05% and 0.08% BAC.
Examples: US & Malaysia: 0.08%; Denmark, Thailand & Philippines: 0.05% and Norway & Sweden: 0.02% BAC

Breath Alcohol Analyzers (BAC Testers)

bac_tester_02.jpg (234170 bytes)A breath analyzer is an instrument that is designed to detect the concentration of alcohol in breath exhaled and using appropriate correction factors calculate the blood alcohol concentration in the blood.
In its simplest form it consists of a sensing element, supporting electronics, a display and a power source. The sensing element used varies widely in specifications and quality and each have pros and cons (see sensors below).
bac_tester_01.jpg (19760 bytes)The sensing element is very important, but so is an assurance that the test is being administered correctly, including flow and volume of the sample. Higher end units incorporate a flow meter that together with time can also be used to calculate volume.
Accuracy is obviously important, especially when used as an enforcement tool, so repeatability and verification using as certified test gas. An inexpensive BAC tester may be fully accurate, however, most that buy them lack the availability of certified test gas and must also understand how to administer the test. Further even with the availability of test gas these units lack the ability to be calibrated should the readings be off.


Sensor Type



Metal Oxide

Extremely cheap
Relatively fast
Acceptable for personal use

Relatively long recovery time (15 minutes between tests)
May lose sensitive over time
Require warm up time

(Fuel Cell)

Acceptable for screening

May be cross sensitive to other gases (i.e. carbon monoxide)
May lose sensitive over time


Wicket fast
Fail safe
Very reliable

Midgrade versions may be cross sensitive to water vapors

False Readings

Whatever sensing technology is used there are always a potential for false positives and false negatives. Given that the sensor is verified and accurate most false readings are because of how and when the test is administered. Volume and flow is the biggest offender. The professional units incorporate a flow meter that can determine adequate flow and volume making it very hard to cheat.

False Positive (higher than actual readings)

When a person takes a breath the depth (volume) and the duration of the breath matters. The deeper the breath is the further into the lungs the air goes and the larger the surface area of alveoli exposed meaning more alcohol vapors are expelled during exhalation. Likewise the longer one holds the breath the more gas is exchanged. While breath analyzers are designed for a deep breath sample keeping that air in the lungs longer than necessary can contribute for a higher than actual reading.
Administering the test too soon after the last sip of an alcoholic beverage can greatly affect the readings. Tests have shown that a 100% sober person will invariably exceed any legal limit if being tested within a few minutes of just one sip. As an example a person pays his bill in a bar and finishes the last of his one and only glass of wine and leaves for his vehicle. If the authorities are waiting to check those leaving the parking lot he is likely to fail. As a rule testing should not be performed within 15 minutes of consuming any alcohol (try to explain that to the police). Along the same lines most mouthwashes and breath sprays will provide the same false positive results as they contain alcohol. bac_tester_03.jpg (91480 bytes)
If unabsorbed alcohol is in the stomach a belch can bring vapors to the mouth and cause higher than actual readings.
Some electrochemical sensors (not all) are cross sensitive to CO, so if one has smoked tobacco within 10 minutes of being tested the test results could be higher than actual.
Diabetics may have elevated levels of acetone in their breath and oxidizing sensors (MOS) may respond to that adding to the readings.

False Negative (lower than actual readings)

A false negative may be desirable to the subject being tested, but often near impossible to achieve. Taking a very shallow breath will provide a lower reading; however, a professional tester with an air flow meter incorporated will invalidate such test. If a tester without airflow monitoring is used this technique may be possible. The person administering the test may be observing the physical movements while taken the breath; to that extent one may try to exhale fully and before starting the inhalation expand the chest half way then inhale and exhale quickly.
Another method that may lower the reading is to hyperventilate for just a few seconds before the test, which may expel stale air in the lungs that may be more saturated with alcohol vapors.
It is worth noting that managing to obtain a lower than actual reading will only affect the readings minimally, but could be the one count that brings one to or below the limit.

jail_01.jpg (37180 bytes)What to do if Testing Positive

If a breathalyzer provides a positive result, then what should you do next?
This obviously depends on the jurisdiction where you are. In the western world you will likely have the right to have a blood test performed which is more accurate. This is an obvious demand if you believe that the test was a false positive. If the test was right at the limit it could be a false positive, but even if it is correctly right over the limit there is always the possibility that enough time elapses so to metabolize just enough alcohol before the test so to bring it down a count.
In countries where the judicial system is not like the west, like Asia, there may not be much one can do but to ask for a blood test and hope for the best.

Best Advice

Don't Drink and Drive!

Contact    Privacy    Terms