Most New Jersey DWI cases involve a breath test on the Alcotest machine. But in some cases — serious crashes, suspected drug impairment, or where breath testing isn’t possible — police seek a blood draw instead. Blood is different from breath in a crucial constitutional way, and that difference has become one of the most important areas of DWI defense.
A blood draw is a search
Taking a person’s blood is a search of the body under the Fourth Amendment. As a general rule, that means police need a warrant — signed by a neutral judge — before they can compel a blood draw, unless a recognized exception applies. This is a stronger protection than the one that applies to breath testing.
What this means for your case
If police took your blood without a warrant, the first question is whether any valid exception applied — a true emergency on the specific facts, or voluntary consent that was actually voluntary. If neither holds up, the blood evidence may be subject to a motion to suppress. Keeping the State’s central piece of evidence out can change the entire trajectory of a case, the same way a successful challenge to a stop or search does in other contexts.
Where blood cases get challenged
Even where a warrant exists, blood evidence has to clear several hurdles:
- The warrant itself — whether it was supported by adequate probable cause.
- Consent — if the State relies on consent, whether it was knowing and voluntary, not coerced.
- The draw procedure — whether it was performed by qualified personnel in a medically acceptable manner.
- Chain of custody and testing — how the sample was stored, handled, and analyzed, and whether the lab’s methods are reliable.
These are the blood-case equivalents of the rigorous requirements that govern breath evidence, which we cover in our piece on Alcotest calibration records.
Refusal and blood are not the same issue
It’s worth understanding that New Jersey’s implied-consent and refusal law applies to breath testing. The rules around compelling blood are governed by the warrant analysis above. The two get conflated, but they’re distinct — another reason these cases benefit from a careful, informed review.
Blood drawn in your DWI case? Have the warrant question reviewed
Whether police obtained a valid warrant — or had a real exception — can determine whether the blood evidence stands or falls. If your DWI case involves a blood draw anywhere in New Jersey, it’s worth a free call to have that question examined closely.
Part of our complete guide: For every related New Jersey offense, claim, and defense in one place, see our NJ DWI Defense Guide.