WASHINGTON – The Supreme Court ruled Wednesday that police usually must try to obtain a search warrant from a judge before ordering blood tests for drunken-driving suspects.

The justices sided with a Missouri man who was subjected to a blood test without a warrant and found to have nearly twice the legal limit of alcohol in his blood.

Justice Sonia Sotomayor wrote for the court that the natural dissipation of alcohol in the blood is generally not sufficient reason to jettison the requirement that police get a judge’s approval before drawing a blood sample.

Missouri and the Obama administration were asking the court to endorse a blanket rule that would have allowed the tests without a warrant.

Eight of the nine justices rejected that plea. Only Justice Clarence Thomas would have held that a warrantless blood test does not violate a suspect’s constitutional rights.

The case stemmed from the arrest of Tyler McNeely in Missouri’s rural Cape Girardeau County. The arresting officer chose not to get a warrant for a blood test. Instead, he drove McNeely to a hospital, where a technician drew blood.