Illinois law considers a driver to be intoxicated per se, or intoxicated according to the law, if he or she has a blood alcohol concentration (BAC) of 0.08% or greater. A blood alcohol concentration of over the legal limit is not always required for a drunk driving arrest, but having a BAC over the limit will certainly make it much harder to beat a DUI charge.
There are two main ways that police officers and prosecutors demonstrate a driver's intoxication level: breath alcohol tests and blood alcohol tests. Blood testing is generally considered to be he most reliable way to determine a person's blood alcohol concentration. However, it is possible for a blood alcohol test to be incorrect.
Contamination of the Blood Sample
Blood alcohol tests involve using a syringe to draw a small quantity of blood from a person's body. Next, the blood is tested in a laboratory to determine the amount of alcohol in the sample. If the blood sample is contaminated, this can throw off the results. For example, if the person who administers the blood test uses an alcohol swab to clean the area and does not let the alcohol dissipate before conducting the blood draw, some of the alcohol may get into the blood sample, artificially increasing BAC.
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