The US Supreme court held that an officer forceably taking blood evidence from a DUI suspect after probable cause but without any exigent circumstances, is an unreasonble search in violation of the 4th Amendment.   The court narrowed the interpretation of prior cases on this point (Schmerber), concluding that the dissipation of alcohol was only one factor to consider in the evaluation of exigent circumstances.  The opinion rejects a per se approach to warrantless blood testing and compels a case-by-case evaluation of the totality of the facts.  

The full case is available here: http://www.supremecourt.gov/opinions/12pdf/11-1425_cb8e.pdf