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How Blood Alcohol Content (BAC) is Measured


BAC (Blood Alcohol Content) is, put simply, a measure of the percentage of alcohol present in your bloodstream. The main reason BAC levels are measured is to ensure a person’s ethanol levels are lower than the legal or acceptable limit in any given circumstance. Interestingly, according to Gilbert DUI attorney Charlie Naegle, the level deemed “acceptable” will vary depending on what country you are in. Additionally, the unit of measurement used to determine and express blood alcohol concentration will vary depending on what country you are being tested in.

In the United States, BAC measurements are calculated by dividing the mass (in grams) of ethanol in the body by 100 milliliters of blood, then converting that number into a percentage. The legal intoxication limit in the state of Arizona (and most other states) is .08%. By this calculation, for every 100 milliliters (or 1dL) of blood in your body, there must be less than 8 grams of alcohol present in the bloodstream. Three ways commonly used to determine a person’s BAC include breath, blood, and urine testing.

1. Breath Testing – Breathalyzers are the most common tool used by police officers to determine if drivers are driving under the influence because they are simple to use, easy to carry and transport, and produce rapid results. The device can immediately detect the alcohol content of the air in your lungs because alcohol is stored as vapor once consumed and does not absorb immediately. The breath measurement is then converted into blood alcohol content using a scientifically derived ratio of 21,000:1. In other words, 21,000 ml of air from your lungs will contain the same amount of alcohol as 1 ml of your blood.

It is possible to estimate your own BAC level with web calculators or store bought devices, but since these tools do not account for differences in body type and tolerance level, (especially if using cheap substitutes to professional grade equipment), there is room for error in the outcome. While breath testing gives immediate results, breath testing is not the most accurate determinant of BAC. If you have been unfairly accused of having a BAC level above the percentage allowed by law, contact Gilbert DUI attorney Charlie Naegle to represent your case.

2. Blood Testing – Medical analysis of a blood sample is a much more accurate way to measure blood alcohol content. However, since drawing blood is an invasive process, which requires consent and more time to produce results, blood testing is not performed on the side of the road to determine DUI charges. However, if an officer has probable cause s/he can require your consent to get a blood test at a later time. Refusal to consent will usually result in greater consequences.

3. Urine Sampling – Urine tests are equally as invasive as blood tests and are more likely to produce inaccurate or “false positive” results. As BAC levels in urine can be adversely affected by time, and alcohol can remain in a person’s system for longer than the period of impairment, this method is not an ideal way to determine if a person is impaired at the time of a specific incident. This method is more effectively used to determine that previously convicted individuals are refraining from the use of alcohol, as per their court sentence.

Getting Assistance from a Gilbert DUI Attorney

Gilbert DUI attorney Charlie Naegle can successfully diminish or dismiss your criminal charges while representing you fairly in court. Call the Naegle & Crider Criminal Defense Attorneys today to schedule an initial consultation.

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