In what circumstances will police be required to obtain blood samples from a driver under the influence of alcohol?

In Schmerber, supra, 384 U.S. 757, 770, the court recognized that the natural dissipation of alcohol in a person's blood could be an exigent circumstance requiring taking blood without consent or a warrant. The court accepted that alcohol in a person's blood stream disappears at a fairly predictable rate after drinking. Thus, delays in obtaining blood samples may result in lost evidence which is relevant to whether the person was under the influence of alcohol while driving. (People v. Thompson (2008) 38 Cal.4th 811, 825.)

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In order to determine if police acted reasonably in relying on exigent circumstances we must look to the totality of the circumstances. (Ohio v. Robinette (1996) 519 U.S. 33, 39.)