Absorption, Effects, Metabolism & Testing
Introduction of Alcohol to the
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
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
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
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)
mixers will cause a faster rate
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.
System & Alcohol in Breath
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
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
What is BAC
BAC is an abbreviation of
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
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
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.
Acceptable for personal use
recovery time (15 minutes between tests)
May lose sensitive over time
Require warm up time
Acceptable for screening
May be cross
sensitive to other gases (i.e. carbon monoxide)
May lose sensitive over time
Midgrade versions may be cross sensitive to water
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
False Positive (higher than actual
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
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.
If unabsorbed alcohol is in the stomach a belch can
bring vapors to the mouth and cause higher than actual
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
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
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
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
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.
Don't Drink and Drive!