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Understanding the importance of a “BAC” in DUI matters

On Behalf of | Jan 9, 2024 | DUI/DWI |

One of the most common terms used by police and other law enforcement personnel in connection with a person suspected of driving while intoxicated is “BAC”. The acronym means “blood alcohol content.” Virtually every state including Michigan has enacted a statute that defines a particular BAC as the dividing line between sobriety and intoxication.

How is BAC calculated?

A person’s BAC can be determined in one of multiple ways:

  • A sample of person’s blood is subjected to chemical analysis in a facility with suitable facilities (usually a hospital) to measure the amount of alcohol that has been absorbed by the person’s blood stream; or
  • the driver submits to a test involving a hand-held device – usually referred to as a “breathalyzer” –  that uses a sample of the person’s breath to measure the amount of alcohol in the person’s blood stream.
  • A third test, known as a “field sobriety test,” can be used to test for intoxication, but the test does not involve the concentration of alcohol in the blood stream and does not produce a BAC measurement.

Limitations on testing

Courts have ruled that a law enforcement officer cannot subject a person to a blood test without first obtaining a search warrant. On the other hand, because the breathalyzer test does not involve the violation of the defendant’s person, Michigan and other states have passed laws that state that any person who operates a motor vehicle on Michigan’s highways has implicitly consented to a breathalyzer test if a law enforcement officer has reasonable cause to believe that the person is intoxicated. (Most such laws are referred to as “implied consent” laws.)

The importance of a BAC

In Michigan, a person’s BAC has a direct bearing on determining whether they may have been driving while intoxicated. The BAC that divides sobriety from intoxication for persons over the age of 21 is 0.08%. The maximum BAC allowed for persons under the age of 21 is 0.02%.

Astute defense attorneys have developed several methods for challenging the results of a breathalyzer tests. Retaining such a lawyer may prevent a verdict of OWI and the ensuing penalties.