Following a person’s arrest for a DUI/DWI criminal offense, police officers will ask the accused/defendant to submit to a blood test or blood draw in which a qualified person such as a nurse at the police station or hospital will draw the defendant’s blood (usually from the arm) into a vial to be tested for alcohol concentration and ultimately to determine whether the person is per se intoxicated. Per se intoxication is intoxication by definition—as defined in the state’s statutes, which is often a blood alcohol concentration (BAC) of .08 or higher.

All states have implied consent laws that make a driver’s consent or agreement to submit to a blood, breath, or urine test (a chemical test) when requested by a law enforcement officer a condition of the driver’s acceptance of a driver’s license offered by the state. Despite implied consent laws, in 2013 the United States Supreme Court held that if a person refuses to submit to having their blood drawn the police cannot draw the blood by force without a search warrant, as required under the Fourth Amendment to the United States Constitution. But more recently the Supreme Court upheld a nonconsensual blood draw of an unconscious person suspected of driving under the influence—based on the state’s implied consent laws and the exigent circumstances exception to the Fourth Amendment's warrant requirement.

And if a driver refuses to take a blood or breath test there are other consequences even if the police do not secure a search warrant for the blood draw—including admission of the refusal in evidence at trial, fines, penalties, and automatic suspension of the driver’s license for a year or more.

In Missouri, the legal limit for blood alcohol concentration (BAC) is .08, and driving with a BAC at or above this level is considered per se intoxication. Under Missouri's implied consent law, drivers have implicitly agreed to submit to chemical tests (blood, breath, or urine) for the purpose of determining BAC when lawfully arrested for a DUI/DWI. Refusal to submit to such testing can result in evidence of the refusal being admitted at trial, fines, penalties, and an automatic suspension of the driver's license for one year. Following the 2013 U.S. Supreme Court decision, police officers in Missouri cannot forcibly draw blood without a search warrant, unless exigent circumstances exist, such as the suspect being unconscious, to comply with the Fourth Amendment. However, even without a warrant or a blood test, a driver can still face consequences for refusing the test.