In early February 2017, the Arizona Supreme Court clarified the requirements that must be met in order for a particular warrant exception to apply in State v. Nissley. The exception at issue, called the blood draw exception, "requires medical personnel to provide [to law enforcement] upon request a portion of any blood sample taken from a patient when the officer has probable cause to believe that the patient had been driving under the influence of alcohol or other drugs." The exception has limitations, and "applies only when the sample is drawn for medical reasons and exigent circumstances exist."

The case arose after Patrick Nissley was arrested in November 2010 for causing an accident that killed one person and injured four others. At the accident scene, Nissley was "delirious, flailing his arms, and screaming incoherently." He had a head wound but was "demanding to be left alone." Paramedics determined that "Nissley could not make coherent decisions for his own care." He was restrained and taken to the hospital where "medical personnel sedated him for treatment and took a blood sample for medical purposes." A police officer arrived at the hospital and "asked for and received a portion of Nissley's blood sample without first procuring a warrant." The blood sample was tested and "revealed the presence of methamphetamine and an active metabolite of heroin." Nissley was ultimately found guilty of reckless manslaughter as well as "endangerment (four counts), and possession or use of narcotic drugs."

Because the officer had not first obtained a warrant, prior to trial "Nissley moved to suppress the results of his blood test for lack of a warrant or a valid exception to the warrant requirement" arguing that "because he was treated against his will, the medical blood draw exception did not apply." The trial court denied his motion "finding that Nissley did not expressly reject treatment and that the exception applied." Nissley subsequently appealed this decision and the Arizona Supreme Court took up the case.

The high court had previously outlined when blood draws were permitted under the constitution, stating draws are allowed if "(1) probable cause existed to believe that the person was driving under the influence, (2) exigent circumstances were present, and (3) the blood was drawn by medical personnel for a medical reason." The court noted that the mere dissipation of blood from the body was not enough for exigency, per prior court cases. However, Nissley hadn't contested this issue but rather had stated a warrant was needed because he had not wanted medical treatment.

The court concluded that "in addition to showing probable cause, exigency, and that blood was drawn in the course of medical treatment for medical purposes, the state must prove that a blood sample obtained under the medical blood draw exception was drawn in compliance with the defendant's right to direct his or her own treatment."

The court stated that "the [S]tate must show that the defendant freely and voluntarily consented to treatment, " with the exception of when the defendant is "incapable of providing consent." The consent can be express or implied, and determining if it was given will be based on a totality of the circumstances.

Thus the court added a fourth requirement that must be met for the blood draw warrant exception, namely, "(4) the provision of medical services did not violate the suspect's right to direct his or her own medical treatment."

The court then vacated the court of appeals decision and remanded the case back to the trial court in order for that court to determine "whether law enforcement lawfully obtained the blood sample." If the sample was not properly obtained, the Supreme Court stated that the trial court "must vacate Nissley's convictions and sentences, suppress the blood alcohol evidence, and order a new trial."