[I]n a situation in which the warrant process will not significantly increase the delay before the blood test is conducted because an officer can take steps to secure a warrant while the suspect is being transported to a medical facility by another officer, . . there would be no plausible justification for an exception to the warrant requirement.
Hence, the Court disagreed with the State of Missouri’s argument that an exigency necessarily exists in any alcohol-related blood test given because that blood-alcohol content rapidly diminishes with time. SCOTUS agreed, however, that significantly delaying a blood test to obtain a warrant would, "negatively affect the probative value of the results."