*606This case raises the question whether, when a driving under the influence (DUI) suspect is injured in an accident and taken to the hospital, the arresting officer needs to obtain a warrant before arranging for the suspect's blood to be drawn for blood alcohol content (BAC) testing. The trial court answered this question in the negative on the facts of this case, denying a motion to suppress BAC evidence. We think the trial court was too quick to find exigent circumstances here, and in the published portion of our opinion conclude that the blood draw was inconsistent with the Fourth Amendment. However, we find the error in this case to have been harmless, and in the unpublished portion of the opinion also reject appellant Matthew Enrique Meza's other challenges. We affirm Meza's convictions for driving under the influence causing injury, and for driving with a BAC of 0.08 percent or more causing injury, in violation of Vehicle Code section 23153, subdivisions (a) and (b).
FACTUAL AND PROCEDURAL BACKGROUND
On the afternoon of September 1, 2013, Meza called his girlfriend and told her he would finish his beer and his golf game and come see her. An hour or more later, about 5:30 p.m., he arrived at her house in Lafayette, driving his own car. After half an hour, they left in her car. Meza was driving. She asked him to drive because she was feeling unwell, and after initially declining he agreed. She saw no symptoms that he was under the influence, and he consumed no alcohol in her presence that evening.
Attempting to keep up with a fast car in the lane next to them, Meza began to speed. At one point where the posted speed limit was 45 miles per hour, he was driving at least twice the speed limit. His girlfriend told him to slow down. As he applied the brakes, the car began to fishtail and he lost control. The car catapulted across the median and on-coming traffic, and fell down an embankment. It was about 6:28 p.m. An off-duty California Highway Patrol sergeant who saw the crash went to check for survivors, and saw Meza emerge from the driver's side of the car.
Concord police officer David Kasid arrived and, with Meza's help, extracted the injured passenger, dragging her to safety ahead of a grass fire that had started under the car. Officer Kasid noticed a slight odor of alcohol on Meza, information that he relayed to Concord police officer Danielle Cruz when additional officers arrived on scene. Officer Kasid then continued with the accident investigation, while *897Officer Cruz pursued the intoxication investigation. A third police officer helped with traffic control, and a corporal in the Concord Police Department came to assess the scene. *607Officer Cruz had a brief conversation with Meza while Meza was waiting to be treated by emergency medical personnel. She asked him what had happened, and smelled "a moderate odor of alcoholic beverage coming from his mouth" as he responded. She noticed blood-shot and watery eyes, which she knew could be a symptom of alcohol consumption, or potentially a head injury. Because Meza was complaining of neck and back pain, Officer Cruz did not ask him to participate in field sobriety tests. She concluded, based on the evidence she had, that he should be arrested for driving under the influence. When an ambulance took Meza and his passenger to the John Muir Medical Center in Walnut Creek, she followed.
At the hospital, Meza had his blood drawn twice. Brenda Leatham, the hospital's lab operations manager, testified that at 7:08 p.m. the hospital drew blood, as they do for all trauma patients, so that doctors will know how to treat patients appropriately. Half an hour later, the hospital had test results. They measured Meza's BAC at 0.148 percent. Then at 8:25 p.m., a phlebotomist summoned by Officer Cruz drew Meza's blood. Joaquin Jimenez, a forensic alcohol expert from the county crime lab, tested this blood sample and measured its BAC at 0.11 percent.
Officer Cruz never attempted to get a warrant before directing the phlebotomist to draw Meza's blood for forensic purposes. She was aware of the United States Supreme Court's decision in Missouri v. McNeely (2013)
The district attorney initiated criminal proceedings and, after a preliminary examination, filed a felony information against Meza. At the preliminary examination, the court heard evidence and ruled on Meza's motion to suppress the test results from the second, police-initiated blood draw. The trial court rejected the prosecutor's argument that Meza's actual or implied *608consent authorized the warrantless blood draw, but nonetheless denied Meza's motion. Citing Schmerber v. California (1966)
Jury trial began on October 26, 2015. The People presented the testimony of officers Kasid and Cruz, of laboratory scientists Leathem and Jimenez, and of Meza's passenger and other percipient witnesses *898to his driving. The defense cross-examined witnesses but presented no affirmative case.
The trial testimony of the laboratory scientists delved into several technical subjects. Leatham explained the procedures followed in drawing and testing Meza's blood to ensure accuracy in the hospital's blood test results, and Jimenez of the crime laboratory testified similarly regarding the forensic blood draw. Leatham testified that, although she did not know the extent to which the hospital's procedures complied with Title 17 regulations for forensic alcohol analysis, the hospital's procedures were sufficiently rigorous that doctors relied on the test results in making treatment decisions.
Jimenez testified to two factors that explain why the two BAC test results differed. First, the county crime laboratory tests whole blood, meaning a blood sample that includes both blood plasma and other cellular material, whereas medical testing is usually (and was in this case) performed on the blood plasma alone. When other cellular material is excluded, the test results from blood plasma usually yield slightly higher numbers, compared to testing from whole blood. Jimenez explained that a test performed from blood plasma produces a number that is higher by a ratio of about 1.1 to 1, or 1.3 to 1, relative to a test from whole blood, with the precise ratio depending on the person whose blood is being tested. Based on what he considered a standard ratio, 1.15 to 1, Jimenez converted Meza's 0.148 hospital test result from blood plasma to 0.128 percent, if the test had been from whole blood as is required for forensic alcohol testing.
Second, Jimenez explained that the human body eliminates alcohol over time, so one would expect the forensic test of Meza's BAC, from a sample taken an hour-and-a-quarter after the hospital's blood sample, to produce a lower reading. Calculating backwards from the 0.11 percent result obtained from Meza's blood drawn at 8:25 p.m., Jimenez estimated Meza's BAC at the time of the accident two hours earlier. He made some assumptions in performing this calculation: that Meza had consumed no alcohol since arriving at his girlfriend's home at 5:30 p.m., and that Meza's body eliminated alcohol at the average rate of 0.015 percent per hour. Based on these *609assumptions, he calculated Meza's BAC at the time of the accident as 0.14 percent, with a margin of error of 0.01 percent. This value is well above the legal limit of 0.08 percent.
Jimenez also testified that whenever an individual's BAC is at or above 0.08 percent, he or she is too impaired to drive safely. He testified that this is not only his personal opinion, but a consensus in the scientific literature that has been endorsed by the American Medical Association, the National Highway Safety Administration, and the National Safety Council.
On November 2, 2015, the jury convicted Meza on both felony counts. In count 1, he was convicted of driving under the influence causing injury. ( Veh. Code, § 23153, subd. (a).) In count 2, he was convicted of driving with a BAC of 0.08 percent or more causing injury. (
The court sentenced Meza to six years in state prison, and Meza timely appealed.
DISCUSSION
I. Motion to Suppress Blood Test Results
In reviewing the trial court's denial of Meza's motion to suppress, we defer *899to the trial court's factual findings where they are supported by substantial evidence, but " ' "exercise our independent judgment in determining the legality of a search on the facts so found." ' " ( People v. Tully (2012)
Under the Fourth Amendment to the United States Constitution, a warrantless search is per se unreasonable unless the People prove that the *610search comes within a recognized exception to the warrant requirement. ( People v. Laiwa (1983)
On grounds of exigent circumstances, the United States Supreme Court more than 50 years ago approved of a warrantless blood draw at the direction of a police officer investigating a driving under the influence case. ( Schmerber , supra ,
Four months before the accident in this case, the United States Supreme Court revisited Schmerber , in another DUI case where the prosecution argued exigent circumstances. ( McNeely , supra , 569 U.S. at p. 145,
Because Meza's case and Schmerber both involved drivers injured in an accident and taken to the hospital for medical care, the trial court saw strong parallels between the two cases. We think the court overlooked dispositive differences. First, while the decision in Schmerber mentions only one police officer involved in the arrest and investigation of that case, in this case there were at least four officers who responded to the accident scene. (See Schmerber , supra , 384 U.S. at pp. 769-771,
On the record before us, the People have not established that exigent circumstances prevented the Concord Police Department from obtaining a warrant before having Meza's blood drawn. Officer Cruz did not even try to get a warrant, presumably because she thought Meza's acquiescence constituted consent.
If the court were to conclude on this record that exigent circumstances excuse law enforcement from getting a warrant, it would be hard to imagine a case requiring a warrant for a blood draw when a DUI suspect is taken to the hospital. We would be creating, sub rosa , a rule that exempts accident cases from the totality-of-the-circumstances inquiry that McNeely requires, and we would be ignoring McNeely 's point about the availability of electronic warrants. ( McNeely , supra , 569 U.S. at pp. 154-156,
Where, as here, an error is of constitutional dimension, we excuse it as harmless only if we are persuaded beyond a reasonable doubt that it did not contribute to the guilty verdicts. ( Chapman , supra , 386 U.S. at p. 24,
II. Other Challenges to the Convictions
DISPOSITION
The judgment of the trial court is affirmed.
We concur:
Kline, P.J.
Richman, J.
Judge of the Alameda County Superior Court, assigned by the Chief Justice pursuant to article VI, section 6 of the California Constitution.
Evidence from the hospital's blood test was not before the court at this hearing.
The trial court rejected that theory (see Bumper v. North Carolina (1968)
See footnote *, ante .
