In most states, you cannot choose a blood test instead of the test the officer selects during a DUI stop. The law enforcement officer typically decides which type of chemical test you’ll take, whether that’s breath, blood, or urine. Refusing the officer’s chosen test because you’d prefer a different one can count as a refusal, triggering automatic penalties like a license suspension. That said, some states do allow you to request an additional independent test after completing the officer’s test, and the rules vary significantly by jurisdiction.
Who Picks the Test: You or the Officer?
The officer chooses. Under most state laws, it’s the law enforcement officer who determines which chemical test to administer. Kansas statute spells this out explicitly: “the law enforcement officer shall determine which type of test is to be conducted or requested.” This is the standard approach across most of the country. Breathalyzers are the most common choice at the roadside because they’re fast, portable, and don’t require medical personnel.
If the officer asks you to take a breath test and you refuse because you’d rather have blood drawn, that refusal carries consequences. Most states treat any failure to “submit to and complete” the requested test as a refusal, regardless of your reason. Penalties typically include an automatic license suspension of one year, sometimes with no option for a restricted license during that period. These penalties kick in through the DMV’s administrative process, separate from whatever happens in criminal court.
Implied Consent and What It Means for You
Every state has an implied consent law. By driving on public roads, you’ve already agreed in advance to submit to chemical testing if an officer has probable cause to believe you’re impaired. New York’s version is typical: “when you drive a car in this state you are considered to have already given your consent to take this type of test.” This doesn’t mean you’ll be physically forced to take a test in every situation, but it does mean refusing comes with built-in penalties that apply even if you’re never convicted of DUI.
Implied consent covers blood, breath, urine, and in some states saliva testing. The consent is to whatever test the officer selects, not whichever one you’d prefer.
When Police Use Blood Tests Instead of Breath
Officers do order blood tests in certain situations, even if you didn’t ask for one. Blood draws are common when the officer suspects drug impairment rather than alcohol, since a breathalyzer only measures alcohol. They’re also used when a breath test isn’t practical, such as when a driver is unconscious after a crash or when a breathalyzer isn’t available.
The U.S. Supreme Court addressed forced blood draws in Missouri v. McNeely, ruling that police generally need a warrant before drawing blood without consent. The natural dissipation of alcohol in the bloodstream doesn’t automatically create an emergency that bypasses the warrant requirement. Officers must look at the totality of the circumstances. In practice, this means officers often get electronic warrants quickly, sometimes within minutes, or rely on the driver’s implied consent.
Blood draws must be performed by authorized medical personnel. Depending on the state, that can include physicians, nurses, trained emergency medical technicians, or in some jurisdictions, law enforcement officers who’ve completed a specialized phlebotomy certification program. NHTSA has developed a formal toolkit for law enforcement phlebotomy programs, reflecting how common officer-performed draws have become in some states.
Your Right to an Independent Test
Here’s where you may have more power than you think. Many states give you the right to request an independent blood test after completing the officer’s chosen test. This is a critical distinction: you can’t substitute the officer’s test with your own, but you can add a second one.
Pennsylvania law, for example, requires that test results be released “upon request of the person tested, his attorney, his physician or governmental officials or agencies.” Several states go further and require officers to inform you of this right or to help facilitate an independent test at a nearby hospital or medical facility, though you’ll usually pay for it yourself.
An independent blood test can be valuable for your defense. If there’s a meaningful discrepancy between the officer’s breathalyzer reading and your independent blood result, your attorney can use that gap to challenge the prosecution’s evidence.
Why Blood Tests Are Considered More Accurate
Blood tests measure alcohol concentration directly from a blood sample, while breathalyzers estimate blood alcohol from the alcohol content in your exhaled breath. That estimation introduces variability. A study comparing breathalyzer results to blood test results in Wisconsin found that breathalyzer readings came in lower than the blood result by more than 0.01 g/210 L about 61% of the time, matched within that margin 33% of the time, and read higher than the blood result only 6% of the time.
That variability is one reason defense attorneys sometimes prefer blood evidence. Breathalyzer readings can be influenced by factors like mouth alcohol from recent burping or acid reflux, device calibration issues, and breathing patterns. Blood tests aren’t immune to challenges either, but the sources of error are different and often easier to identify.
How Blood Samples Can Be Challenged
A blood test result isn’t automatically bulletproof evidence. The sample has to be collected, stored, and analyzed following strict protocols, and any break in that chain creates an opening for a defense challenge.
Storage matters enormously. Best practice standards recommend blood samples be kept below 8 degrees Celsius (46 degrees Fahrenheit) before testing. Refrigeration slows bacterial growth and metabolic activity that can alter the alcohol concentration in the sample. If a blood tube sits at room temperature for an extended period, bacteria can ferment sugars in the blood and actually produce alcohol, artificially inflating the result.
To counteract this, blood collection tubes contain sodium fluoride as a preservative. California’s regulations under Title 17 require that “samples taken for forensic alcohol analysis shall be collected and handled in a manner in which the identity and integrity of the samples shall be maintained through collection to analysis and reporting.” When samples aren’t properly refrigerated, they need higher amounts of preservative to remain reliable. Defense attorneys regularly scrutinize whether the tube contained adequate preservative and whether the sample was refrigerated promptly.
Chain of custody is the other common target. After a blood draw, the tubes must be marked, sealed into an inner container, placed into an outer transport container, and sealed again with a tamper-evident shipping seal. Every person who handles the sample must be documented. A gap in that documentation, or evidence that the seal was broken, can be enough to get a blood result excluded from evidence.
What to Do During a DUI Stop
Take the test the officer requests. Refusing because you want a different test type will almost certainly be treated as a refusal, costing you your license for a year or more regardless of whether you were actually impaired. After you complete the officer’s test, ask clearly whether you have the right to obtain an independent test. Say it out loud so it’s captured on any recording. If the officer says yes, ask to be taken to a medical facility or to have a qualified person draw your blood as soon as possible, since your BAC changes over time.
Write down everything you remember as soon as you can: what time the stop happened, what time the test was administered, what the officer told you about your options, and whether you were informed of your right to independent testing. These details become important if your case goes to court and you or your attorney need to challenge the procedures used.