Wisconsin case law has established that law enforcement officials can force a drunk driving suspect to provide a blood sample without first obtaining a warrant in exigent circumstances. The reason behind this ruling has to do with the imminent destruction of evidence. As the body metabolizes alcohol, it removes it from the bloodstream, lowering a person's blood alcohol content.
Law enforcement officers want to conduct the blood test as close to the alleged instance of drunk driving as possible to get a definitive reading of the suspect's blood alcohol content. The longer one waits to administer the test, the reasoning goes, the more likely it becomes that the suspect's body will remove enough alcohol from the bloodstream to cross beneath the legal threshold for DUI.
But there are other considerations in play when law enforcement takes a blood sample without the suspect's consent and without a warrant--namely the suspect's Fourth Amendment rights to be free from unreasonable searches and seizures. These competing considerations will be sorted out by the U.S. Supreme Court, which has agreed to take a DUI case from Missouri where officers ordered a warrantless drawing of blood.
Prosecutors in the case argued that the imminent destruction of evidence--that is, the alcohol in the suspect's bloodstream--provided circumstances sufficient to draw the blood without obtaining a search warrant. Missouri's Supreme Court disagreed, and now the case is headed to our land's highest court, where the decision could have an effect on drunk driving cases here in Wisconsin and around the nation.
Source: Christian Science Monitor, "Forced blood test for a drunk-driving suspect? Supreme Court to step in," Warren Richey, Sept. 25, 2012