What prompts an officer to conduct a blood test for impairment?

A blood test for impairment is typically prompted by the results of a failed field sobriety test. When an officer observes a driver completing a series of standardized tests designed to assess their physical and cognitive abilities, a failure in these tests strongly indicates that the driver may be under the influence of substances that impair their ability to operate a vehicle safely. Field sobriety tests measure balance, coordination, and judgment, and if a driver does not pass these tests, it provides probable cause for the officer to conduct more intrusive testing, such as a blood test, to determine the level of impairment and the specific substances involved.

While traffic violations, the presence of alcohol in the vehicle, and random roadside checks can lead to various investigative actions, none are as directly indicative of impairment as the results from a field sobriety test, which explicitly demonstrate a driver’s inability to perform tasks that are crucial for driving safely.