Blood alcohol content is a measure of how much alcohol is in your body; it is also referred to as a BAC. Each state in the country applies various charges related to driving while intoxicated based on how high your BAC limit is if law enforcement tests it. In most states, including New York, charges are possible beginning at a .08 percent BAC.
Blood alcohol content is measured in three ways: a breath test, blood test or urine test. Because it can be performed easily in the field, the breath test is one of the most common methods of detection used by law enforcement. The test is conducted with a machine known as a Breathalyzer, which is lightweight and easy to carry in a patrol car. A person blows into the Breathalyzer and the amount of alcohol expelled in from the lungs and into the air is measured. While Breathalyzers are considered legally accurate enough to result in charges, averaging and application of breath tests to all individuals can result in inaccurate readings for some.
Blood sampling is the most accurate way to measure BAC levels, though it usually requires a person agree to the sampling and be transported to a place where the sampling can be done. Field officers are not usually equipped or trained for such purposes. One thing worth noting is that refusal of these tests can result in charges too, often with bigger fines or consequences than a first-time DWI charge.
Urine testing is the least accurate way to measure BAC, so it is only used when access to the other types of tests is not available. Urine tests are heavily impacted by time in relation to a person’s last drink, and validation testing might be required for any sample.
No type of BAC test is 100 percent accurate all of the time, which means defenses against test results do exist. Understanding how to defend against BAC results is a critical component of DWI criminal defense.
Source: BAC Track, “Three Types of BAC Testing,” accessed Dec. 18, 2015