The U.S. Supreme Court recently issued its ruling on an important case involving a warrantless blood test on an individual suspected of drunk driving. The Court said a warrant must be obtained before performing a blood test on an individual against his or her wishes except when it is reasonable and urgent to forgo a warrant, which depends on the circumstances of the case.

Do police ever need a warrant to draw blood from a drunk-driving suspect?

The case originated in Missouri, where a man was pulled over for speeding. The officer noted signs of intoxication and asked the man to perform field sobriety tests, which he failed. After refusing to perform a breath test, the man was arrested and taken to a hospital for a blood test to determine his blood alcohol content, without his consent. The blood test revealed a BAC of 0.15 percent nearly half an hour after the man was stopped.

When the prosecution attempted to present the blood test evidence in court, the trial court ruled that the results were inadmissible. Because the officer had not first obtained a warrant for the test, the forced blood test was a violation of the Fifth Amendment to the Constitution’s guarantee against unreasonable searches and seizures, and therefore, the evidence could not be used, it said.

The state of Missouri appealed the decision, arguing that, because alcohol dissipates from the blood so quickly, “exigent circumstances” exist that permit police to act without a warrant. Missouri and other supporters claimed that a warrant should never be required for blood tests on drunk-driving suspects because it is vital to perform a timely test and obtaining a warrant may take too long.

The Supreme Court says yes, most of the time

The Supreme Court ruled that police do not have the absolute ability to perform a blood test without an individual’s consent without a warrant. In the opinion, Justice Sonia Sotomayor wrote that police must obtain a warrant when it will not significantly undermine the efficacy of the search, and that, “whether a warrantless blood test of a drunk-driving suspect is reasonable must be determined case by case based on the totality of the circumstances.”

The Court acknowledged that a delay in obtaining a warrant in some cases may lead to the destruction of evidence as the suspect’s body metabolizes the alcohol, but the question of whether forgoing a warrant is reasonable depends on the unique circumstances of the individual case. The opinion also reasoned that obtaining a warrant quickly is possible in many circumstances, using technology like emails to judges, for example.

This ruling limits the power of police officers to perform warrantless blood tests and holds steady against the erosion of individuals’ privacy rights in motor vehicles. If you have been arrested on suspicion of drunk driving, contact a criminal defense attorney with experience in drunk driving cases to begin your defense.