Chemical Tests and BAC

When you are suspected of driving under the influence, the police will require you to submit to a chemical test to verify the presence of alcohol and/or drugs in your blood. You will be given the choice of submitting to a breath test or a blood test to determine your Blood Alohol Content (BAC). When you were issued a California drivers license, you agreed to these tests under the “implied consent” law. You will not be able to speak to an attorney prior to the test. It may be better to consent to the test than to refuse because the DMV will impose automatic penalties for your failure to comply with the “implied consent” rule.

According to current California law, it is unlawful for any person whose BAC is 0.08 percent or more to drive a vehicle. How can you estimate your Blood-Alcohol Level (BAC)? Use our BAC Calculator.

In California, chemical tests involve a choice of breath or blood; urine was discontinued in 2000, except where neither breath nor blood are available. Breath machines used in California are susceptible to numerous problems and none of them are reliably accurate. Blood analysis is considerably more accurate, although possible problems exist as well. Urinalysis is the least reliable test for blood-alcohol concentration.

There are testing inconsistencies and variations depending on the person and the environmental conditions. For example:

Weight: In general, the less you weigh the more you will be affected by a given amount of alcohol. Alcohol is affected by the percentage of water in the body. Typically, a larger individual will have a lower BAL reading even though the actual amount of alcohol consumed is the same as a smaller person.

Gender: Generally women tend to have a higher percentage of body fat, and thus a lower percentage of body water, and if a man and a woman of the same weight ingest the same amount of alcohol the woman will tend to achieve a higher alcohol concentration. However, certain studies have shown that women eliminate alcohol from their bodies at a rate 10% greater than that of men which may counteract gender differences in body composition.

Age: Total body water also tends to decrease with age, so an older person will be more affected by the same amount of alcohol. Blood alcohol concentrations may be up to 10% higher in an older person even though the amount of alcohol consumed was the same.

Body Temperature: The widely used blood-to-air partition ratio of 2100:1 is based on a normal body temperature of 98.6°F. A higher body temperature will overestimate the actual BAC because of the higher volatility (or vapor pressure) of liquids like alcohol at a higher temperature. Therefore, a person with a body temperature of 100.4°F, and with an actual blood alcohol of 0.0935%, will register a value of 0.10% by the breath test. If you have a fever and your body temperature is elevated, you may give a higher reading.

Cellular Composition Of Blood: Blood contains suspended cells and proteins, and is therefore only a partial liquid. The partition ratio of 2100:1 is based on an average cell volume of blood of 47%. Cell volume values range from 42 to 52% in males and 37 to 47% in females. Therefore, a person with a lower cell volume will have a falsely elevated blood alcohol based on a breath test.

Level Of Fitness: For people of the same weight, a well muscled individual will be less affected by the same volume of alcohol than someone with a higher percentage of fat. Body fat will not absorb as much alcohol as muscle since it contains less water. The less alcohol your body absorbs, the more alcohol will go into the bloodstream.

Exercise: Strenuous exercise can increase your breathing rate thus increasing the flow of alcohol into the lungs. This can cause the alcohol to be expelled at a greater rate than if you were sedentary. Hyperventilation can have the same effect as strenuous exercise.

Why Breathalyzers Are Used To Test Blood Alcohol Content (BAC)

Alcohol that a person drinks shows up in the breath because it gets absorbed from the mouth, throat, stomach and intestines into the bloodstream. Alcohol is not immediately digested upon absorption or chemically changed in the bloodstream. As the blood goes through the lungs, a predictable amount of alcohol will move into the lungs.

When the alcohol comes in contact with the air in the lungs it evaporates. The concentration of alcohol in the lungs is directly related to the concentration of alcohol in the blood. Exhaling the evaporated alcohol will determine the BAC in your body.

How Breathalyzers Work

Breathalyzers are complex, sophisticated devices that use a combination of chemicals such as sulfuric acid and silver nitrate that, when combined with the air from your lungs, produces chemical changes. The changes are directly related to the blood alcohol content in your body.

Simply stated, there is a tube into which you breathe and this goes into vials containing chemicals. The result of the mixing of breath and chemicals creates a reaction that produces an electrical current. This current moves a dial that then measures the amount of alcohol in your blood stream.

Obviously, the operator of the breath device must be specifically trained to perform the test accurately. The use of breath tests is regulated by Title 17 of the California Code of Regulations and their operators must adhere to its guidelines. The California code of regulations is a complex technical manual.

Understanding the complexity of the equipment combined with the expertise needed to register a “true” reading makes it even more crucial that you do not consent to a portable (roadside) breath test. Make sure that you are tested in a controlled environment by accredited practitioners.

Why Blood Tests Are Used

You will generally have the option of submitting to a breath test or a blood test but under certain situations such as an injury that prevents you from consenting to a breath test, you will be given a blood test. It is often suggested that you choose to take a blood test rather than a breath test because the evidence from a breath test cannot be saved whereas a blood sample can be preserved for independent examination at a later date.

You may think that a blood test is more accurate and while this is the popular belief, many circumstances can alter its accuracy. Only qualified personnel can administer a blood test and, as with breath tests, the California code of regulations must be followed. Many environmental and human factors such as improperly mixed chemicals, contaminated apparatus, etc., can lead to a false reading.

If you are facing DUI or drunk driving charges in California, you need the assistance of an experienced and competent California DUI lawyer.


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