Arizona Supreme Court Clarifies ER Malpractice Proof Standard: What Henke v. Hospital Development of West Phoenix Means for Emergency Medicine Accountability

For years, Arizona hospitals defending emergency room malpractice cases had a powerful procedural weapon: the argument that a plaintiff's expert witness, by using the word "likely" rather than "certainly" or "clearly," had failed to meet the state's elevated evidentiary standard and that the case should therefore be dismissed before it ever reached a jury. The Arizona Supreme Court's unanimous ruling in Henke v. Hospital Development of West Phoenix, Inc. closes that loophole — and in doing so, reshapes the landscape of ER accountability in Arizona.

The Case: Greg Henke and Bacterial Endocarditis

Greg Henke presented to a Banner Health emergency department in West Phoenix with symptoms that his wife, Margarita, and her legal team would later argue were consistent with bacterial endocarditis — a serious infection of the heart's inner lining that, if diagnosed promptly, is treatable with antibiotics and, when necessary, surgery. Bacterial endocarditis can present with fever, fatigue, joint pain, and a new or changed heart murmur. It is a diagnosis that requires clinical suspicion and appropriate workup; it is also a diagnosis that, if missed, can be fatal within days.

According to the allegations in the case, the emergency physicians who evaluated Greg Henke failed to consider bacterial endocarditis in their differential diagnosis, failed to order the blood cultures and echocardiogram that would have been appropriate given his presentation, and discharged him without a diagnosis that would have led to life-saving treatment. Greg Henke died. Margarita Henke filed suit against Hospital Development of West Phoenix, Inc. — the entity operating the Banner Health emergency department — alleging that the emergency physicians' negligence caused her husband's death.

The case proceeded through discovery, and Margarita Henke retained an expert witness — a physician with relevant expertise — who reviewed the medical records and testified that, in his opinion, the emergency department's failure to diagnose and treat bacterial endocarditis "likely" caused Greg Henke's death. The hospital moved for summary judgment, arguing that this testimony was insufficient to meet Arizona's clear and convincing evidence standard for emergency room malpractice cases. The trial court agreed and dismissed the case. Margarita Henke appealed.

Arizona's Heightened Standard for ER Malpractice

To understand the significance of the Henke ruling, it is necessary to understand the legal framework within which it arose. Arizona, like a small number of other states, imposes a heightened evidentiary standard on plaintiffs in emergency room malpractice cases. Under Arizona Revised Statutes Section 12-563.1, a plaintiff alleging malpractice against an emergency room physician or facility must prove their claim by "clear and convincing evidence" rather than the "preponderance of the evidence" standard that applies in most civil cases.

The preponderance standard — the default in civil litigation — requires a plaintiff to show that it is more likely than not (i.e., greater than 50% probable) that the defendant's negligence caused the plaintiff's injury. The clear and convincing standard is higher: it requires the plaintiff to show that the truth of their claim is "highly probable" or "substantially more likely than not." It is a standard that falls between the preponderance standard and the criminal "beyond a reasonable doubt" standard.

Arizona's heightened standard for ER cases was enacted by the legislature as part of a broader effort to address concerns about the availability of emergency physicians in the state — a recognition that the threat of malpractice liability was contributing to physician shortages in emergency medicine and that some additional protection for ER providers was warranted. Similar statutes exist in a handful of other states, including Texas, which requires proof of "willful and wanton negligence" for ER cases — an even higher standard than Arizona's.

The practical effect of Arizona's heightened standard had been, in many cases, to give defense attorneys a procedural tool for dismissing ER malpractice cases before trial. If a plaintiff's expert testified using language that sounded like the preponderance standard — "more likely than not," "probably," or "likely" — defense counsel would argue that this testimony failed to meet the clear and convincing standard and move for summary judgment. Trial courts, uncertain about how to apply the standard to expert testimony, sometimes granted these motions, effectively ending cases that might have had merit.

The Court of Appeals and the Path to the Supreme Court

The Arizona Court of Appeals reversed the trial court's dismissal of Margarita Henke's case, holding that the expert's testimony — that negligence "likely" caused Greg Henke's death — was sufficient to survive summary judgment under the clear and convincing standard. The court reasoned that the clear and convincing standard governs the ultimate burden of proof at trial, not the threshold for surviving a motion for summary judgment, and that the expert's testimony, taken as a whole, was sufficient to create a genuine issue of material fact.

The hospital petitioned the Arizona Supreme Court for review, arguing that the Court of Appeals had misapplied the clear and convincing standard and that allowing "likely" causation testimony to survive summary judgment effectively collapsed the distinction between the preponderance and clear and convincing standards. The Supreme Court granted review — a signal that the justices recognized the significance of the question and the need for a definitive ruling.

The Supreme Court's Ruling: Justice King's Unanimous Opinion

Justice Kathryn H. King, writing for a unanimous court, affirmed the Court of Appeals and held that the expert testimony in Henke was sufficient to connect the alleged negligent conduct to Greg Henke's death. The court's reasoning rested on several key principles.

First, the court held that the clear and convincing standard is a standard of proof — a measure of the persuasiveness of the evidence as a whole — not a linguistic test applied to individual words in expert testimony. An expert who testifies that negligence "likely" caused a patient's death is not automatically failing to meet the clear and convincing standard; the question is whether the totality of the evidence, including the expert's full testimony, the medical records, and all other evidence in the case, is sufficient to establish causation by clear and convincing evidence.

Second, the court held that applying the clear and convincing standard at the summary judgment stage — as the trial court had done — was error. Summary judgment is appropriate only when there is no genuine dispute of material fact. The question of whether the evidence meets the clear and convincing standard is a question for the factfinder — the jury — not for the court on a motion for summary judgment. By dismissing the case because the expert used the word "likely," the trial court had usurped the jury's role.

Third, the court emphasized that medical causation is inherently probabilistic. Physicians and medical experts do not speak in certainties; they speak in probabilities. An expert who testifies that negligence "likely" caused a patient's death is expressing a high degree of probability — a probability that, in context, may well satisfy the clear and convincing standard. To require experts to use specific magic words — "clearly," "certainly," "beyond doubt" — would impose an artificial linguistic requirement that has no basis in the law and would systematically disadvantage plaintiffs whose experts testify with appropriate scientific precision.

The court remanded the case to the trial court for further proceedings consistent with its opinion — meaning that Margarita Henke's case will proceed, and a jury will ultimately decide whether the emergency department's alleged failure to diagnose bacterial endocarditis caused Greg Henke's death.

Implications for Emergency Medicine Accountability in Arizona

The Henke ruling has significant practical implications for ER malpractice litigation in Arizona. Most immediately, it eliminates the procedural tactic of seeking summary judgment based solely on the language used by a plaintiff's expert. Defense attorneys can no longer argue that "likely" causation testimony is legally insufficient; they must instead challenge the substance of the expert's opinion at trial.

For plaintiffs and their attorneys, the ruling means that cases that might previously have been dismissed on procedural grounds will now survive to trial. This is significant not only for the individual plaintiffs whose cases were dismissed, but for the broader accountability function of malpractice litigation. Cases that reach trial create a public record of what happened; they produce verdicts that signal to hospitals and physicians what conduct is unacceptable; and they generate settlements that compensate victims and, in theory, incentivize safety improvements.

For emergency physicians and hospitals, the ruling means that the clear and convincing standard — while still a meaningful protection — is not the near-absolute shield that some had treated it as. Emergency physicians will still benefit from the heightened standard at trial; plaintiffs will still need to present compelling evidence of negligence and causation to prevail. But they will no longer be able to avoid trial simply by arguing that the plaintiff's expert used probabilistic language.

The ruling also has implications for how expert witnesses in Arizona ER malpractice cases will be prepared and presented. Plaintiffs' attorneys will likely continue to use probabilistic language — "likely," "probably," "more probable than not" — but will ensure that their experts' full testimony, taken as a whole, conveys the high degree of probability that the clear and convincing standard requires. Defense attorneys will focus their challenges on the substance of the expert's opinion rather than its language.

The Broader Context: ER Malpractice Standards Nationally

Arizona is one of a small number of states that impose a heightened evidentiary standard on ER malpractice plaintiffs. Texas requires proof of "willful and wanton negligence" — a standard so high that it is rarely met. Georgia, Colorado, and a handful of other states have enacted similar protections. These statutes reflect a legislative judgment that emergency physicians, who must make rapid decisions under conditions of uncertainty, deserve some additional protection from malpractice liability.

Critics of these statutes argue that they create a two-tiered system of accountability in which patients harmed in emergency departments have fewer legal protections than patients harmed in other healthcare settings — a disparity that is particularly troubling given that emergency departments serve disproportionately poor, uninsured, and vulnerable populations. The Henke ruling does not eliminate Arizona's heightened standard, but it does ensure that the standard is applied as a genuine evidentiary requirement rather than as a procedural barrier to access to justice.

The ruling also arrives in the context of a broader national conversation about ER accountability. ER Times' four-part malpractice series has documented $123.8 million in verdicts and settlements in 2024–2026, driven by missed diagnoses, inadequate workups, and premature discharges. The Henke case — a missed diagnosis of bacterial endocarditis — fits squarely within this pattern. The Supreme Court's ruling ensures that cases like Greg Henke's will be decided on their merits, not dismissed on procedural grounds.

What Happens Next: The Henke Case on Remand

The Arizona Supreme Court's remand sends the case back to the trial court for proceedings consistent with the opinion. In practical terms, this means that the trial court must reinstate Margarita Henke's case and allow it to proceed toward trial. The hospital may file additional motions — challenging the qualifications of the plaintiff's expert, seeking to exclude certain evidence, or raising other defenses — but it cannot again seek dismissal on the ground that the expert used the word "likely."

At trial, the jury will hear evidence about Greg Henke's presentation to the emergency department, the standard of care for evaluating patients with his symptoms, the emergency physicians' actual conduct, and the expert's opinion that the failure to diagnose bacterial endocarditis caused his death. The jury will apply the clear and convincing standard — as instructed by the court — and decide whether Margarita Henke has proven her case.

The outcome of the trial is uncertain. The clear and convincing standard is a meaningful hurdle, and the hospital will present its own experts and defenses. But the case will be decided on its merits — which is, the Arizona Supreme Court has unanimously held, exactly what the law requires.