Sometimes, but not automatically. Police generally need a warrant before drawing your blood after a DUI arrest. The fact that alcohol breaks down in your body over time is not, by itself, enough to skip that requirement. Whether a specific warrantless draw was lawful depends on which of a few narrow situations actually applied.

If you are conscious, you choose blood or breath

Under Vehicle Code section 23612, a person who is lawfully arrested for an alcohol-related DUI and capable of completing either test gets to choose blood or breath, not the officer, and the officer has to advise the person of that choice. Refusing a test carries its own license and sentencing consequences, covered on this site’s page about DUI refusal cases, which is a separate question from whether police were allowed to draw blood without asking a judge first.

Why alcohol dissipating is not automatically an emergency

In Missouri v. McNeely (2013), the State asked the U.S. Supreme Court to hold that because alcohol leaves the bloodstream over time, an officer with probable cause of drunk driving may always draw blood without a warrant. The Court refused. It held that the natural dissipation of alcohol may support an emergency exception in a specific case but does not do so categorically, and that whether a warrantless blood test was reasonable must be decided case by case based on the totality of the circumstances. When officers can reasonably get a warrant before the blood draw without significantly undermining the test, the Fourth Amendment requires them to do so. So the specific facts matter, such as how long getting a warrant would actually have taken and whether anything else about the situation made waiting impractical.

Breath and blood are not treated the same

Birchfield v. North Dakota (2016) drew a sharp line: the Fourth Amendment permits a warrantless breath test incident to a drunk-driving arrest, but not a warrantless blood test. The Court reasoned that a needle draw is significantly more intrusive than breathing into a device, so the automatic search-incident-to-arrest justification that covers a breath test does not carry over to blood. A state also cannot make it a crime to refuse a warrantless blood test the way it can for a breath test, though the Court said its ruling casts no doubt on implied-consent laws that impose civil penalties and evidentiary consequences for refusing. If what was taken from you was blood rather than breath, the routine, no-warrant-needed justification for a breathalyzer does not apply on its own.

The unconscious-driver exception

Mitchell v. Wisconsin (2019) addressed a driver whose unconsciousness or stupor required a trip to a hospital or similar facility before police had a reasonable opportunity to give a standard evidentiary breath test. No opinion drew a majority. The lead opinion, joined by four Justices, concluded that in that situation officers “may almost always order a warrantless blood test” without violating the Fourth Amendment, noting that such a driver is likely to have blood drawn for medical reasons anyway; Justice Thomas agreed with the result for different reasons. The lead opinion described a strong presumption, not an absolute rule: it left room for an unusual case in which the driver shows that the blood would not have been drawn if police had not been seeking BAC information, and that police could not reasonably have judged that a warrant application would interfere with other pressing needs or duties.

What this means for your situation

  • If you were conscious, said yes, and were given the admonition required by Vehicle Code 23612: the live question is usually whether that agreement was truly voluntary, a fact-specific issue that depends on exactly what was said and how.
  • If you refused and blood was drawn anyway without a warrant: the state has to point to an exception that fits the facts, such as a genuine case-specific emergency, not simply the general fact that alcohol metabolizes.
  • If you were unconscious or in a stupor and taken for medical care before a breath test could be given: a warrantless draw is likely to be upheld under the Mitchell lead opinion, though not in every case.

How the blood was handled after the draw, including chain of custody, storage, and lab procedure, raises a separate set of questions. An attorney who handles DUI blood test defense can review the police report and timeline to identify which of these situations the state is relying on and whether the facts actually support it. Call the Law Offices of David S. Chesley at (800) 755-5174 to go through what happened in your case.