When can a police officer withdraw blood from the blood of a suspect under the exigent circumstances theory?

Nonetheless, the court upheld the blood withdrawal on an exigent circumstances theory because of the rapid elimination of alcohol from a person's blood. "The officer in the present case, however, might reasonably have believed that he was confronted with an emergency, in which the delay necessary to obtain a warrant, under the circumstances, threatened `the destruction of evidence,' [citation].... Given these special facts, we conclude that the attempt to secure evidence of blood-alcohol content in this case was an appropriate incident to petitioner's arrest." (Schmerber v. California, supra, 384 U.S. at pp. 770-771, 86 S.Ct. 1826.)