The Trombetta advisement is the notice a California officer gives a DUI suspect who takes a breath test: the machine does not save a sample of your breath, and because of that, you may provide a blood or urine sample at no cost that will be preserved for later testing. It comes from Vehicle Code Section 23614, and it exists so you have a fair chance to gather physical evidence for your own defense. The name traces back to the 1984 U.S. Supreme Court case California v. Trombetta, which held that police do not have to preserve breath samples themselves.
What the Officer Must Tell You
Vehicle Code Section 23614 lays out three points the officer is required to convey.1California Legislative Information. California Vehicle Code 23614
First, that the breath-testing equipment does not retain any sample of your breath for later analysis by you or anyone else. The air you blow into the machine is measured instantly and released. Nothing physical is stored.
Second, that because no breath sample is kept, you have the opportunity to provide a blood or urine sample that will be retained at no cost to you.
Third, that the retained blood or urine sample can be tested by either side in any criminal prosecution. The statute also notes that if neither side tests the retained sample, that failure creates no obligation on the other party and does not affect the admissibility of other blood-alcohol evidence.
The exchange usually happens at the station or a mobile testing unit, around the time of the breath test. It is brief, but it sets up a real choice.
Why the Advisement Exists
In California v. Trombetta, 467 U.S. 479 (1984), the Supreme Court was asked whether the Constitution requires police to capture and store a suspect’s breath so the defense can retest it. The Court said no.2Justia Law. California v. Trombetta, 467 US 479 (1984) It found that breath test results carry their own safeguards and that defendants have other ways to challenge accuracy, such as questioning the operator or the machine’s calibration history.
The ruling did not create the advisement. What it did was leave breath samples unpreserved as a matter of federal law. The California Legislature then codified an offer that fills the gap, giving suspects the chance to create physical evidence through a blood or urine sample. That offer is what officers deliver when they read the Trombetta advisement.
The Choice the Advisement Puts in Front of You
Under California’s implied consent law, a lawfully arrested DUI suspect chooses between a breath test and a blood test, with urine available only in limited situations.3California Legislative Information. California Vehicle Code 23612 If you chose blood in the first place, a sample is already being preserved, and the advisement matters less to you.
The advisement matters most when you took the breath test. Section 23614 gives you the additional right to then provide a blood or urine sample that will be collected and retained just as if you had chosen blood from the start.1California Legislative Information. California Vehicle Code 23614 Saying yes costs nothing. Saying no, or not understanding what was offered, means there is no physical specimen tied to your arrest that can be independently analyzed later.
Getting the Retained Sample Tested Later
If a blood sample was collected, Title 17 of the California Code of Regulations requires the agency holding it to keep the remaining portion for one year from the date of collection.4Legal Information Institute. California Code of Regulations Title 17 1219.1 – Blood Collection and Retention That one-year window exists specifically so you can request independent testing.
The mechanism is usually a blood split motion, filed by defense counsel, asking the court to order release of a portion of the stored sample to a private laboratory. Title 17 requires the agency in possession to provide a portion whenever the defendant requests it and sufficient sample remains. The agency keeps the original vial and provides a split in a clean container along with identifying information.
An independent retest can uncover problems with the original analysis, such as a degraded sample, fermentation that inflated the reading, or contamination introduced during collection. Even a result that matches the prosecution’s number has value: it narrows the defense to other issues and keeps the jury from wondering what an independent test might have shown. If you took the breath test and declined the offer to also provide a blood sample, there is nothing to split.
If the Officer Did Not Give the Advisement
A failure to deliver the advisement does not automatically make your breath test results inadmissible. California courts treat it as a procedural safeguard rather than a prerequisite for the test’s scientific validity. The machine still measured what it measured.
The omission is not meaningless, though. A defense attorney can argue that skipping the advisement deprived you of the informed choice Section 23614 guarantees, specifically the chance to provide a retained sample for independent testing.1California Legislative Information. California Vehicle Code 23614 If you would have given a blood sample but were never told you could, the argument is that the missing advisement prejudiced your defense. Whether it succeeds depends on the judge, the facts, and the rest of the evidence.
The argument tends to be strongest when the breath results are close to 0.08 percent and an independent blood test might have produced a different number. There, the missing advisement is a concrete gap the jury can weigh.
If a Retained Sample Is Later Lost or Destroyed
If you did provide a blood sample and the agency loses or destroys it, two constitutional standards apply.
Under California v. Trombetta, if the destroyed evidence had apparent exculpatory value before it was destroyed, and you cannot obtain comparable evidence by other reasonably available means, the government violated your due process rights regardless of intent.2Justia Law. California v. Trombetta, 467 US 479 (1984) That is a high bar. Most lost blood samples do not have obvious exculpatory value before they are tested.
The more common situation falls under Arizona v. Youngblood, 488 U.S. 51 (1988). The Court held that failing to preserve merely “potentially useful” evidence does not violate due process unless the defendant can show bad faith by the police.5Library of Congress. Arizona v. Youngblood, 488 US 51 (1988) Bad faith means the police knew the evidence could help the defense and destroyed it anyway. Negligence or sloppy handling usually will not clear that bar.
Even without a constitutional violation, a missing or degraded sample is useful material for cross-examination. Jurors notice when the government cannot produce physical evidence it was supposed to keep.
What This Means in Practice
If you are arrested for DUI in California and take a breath test, expect to hear the Trombetta advisement. Listen for the offer of a blood or urine sample at no cost, and understand that agreeing to it is what preserves your ability to have physical evidence independently tested during the one-year retention period. If you were not given the advisement, tell your attorney; the omission may not end the case, but it can shape the defense.