Breath and Blood Tests in Texas DWI Cases

And the assumption is only the beginning. Residual mouth alcohol from GERD, acid reflux, or even a recent belch can compromise the reading. So can radio frequency interference, improper operator procedure, and failure to maintain and calibrate the instrument as DPS regulations require. We break down the machine's known weak points in detail on our Intoxilyzer 9000 page.

Blood Tests: Stronger Evidence, Still Beatable

A blood test measures the alcohol or drugs in your actual blood, which is why blood results are generally considered more accurate than breath results. They are far from infallible, though — a blood number is only as reliable as every step that produced it.

Texas law strictly limits who can draw your blood — only physicians, registered nurses, licensed vocational nurses, qualified technicians, or chemists — and it dictates how the sample must be collected, labeled, stored, and transported to prevent contamination or degradation. When those procedures break down, the reliability of the result breaks down with them.

In our experience, the details of the draw and the lab work matter as much as the number itself. The issues we investigate include:

• Improper collection techniques that cause hemolysis, the destruction of red blood cells
• Inadequate refrigeration while the sample was stored or transported
• Contamination from alcohol-based skin swabs used at the draw site
• Chain of custody gaps, where the state cannot fully document how your sample was handled
• Analytical errors at the testing laboratory

Then there is timing. Your blood is not drawn at the roadside — it is drawn later, at the station or a hospital, and your BAC does not stand still in between. If your body was still absorbing alcohol when you were stopped, your BAC may have been lower when you were actually driving and higher by the time the needle went in. The state's number shows where you were at the moment of the draw, not necessarily when you were behind the wheel.

When Police Can Take Your Blood Without Your Consent

In most DWI cases, if you refuse both breath and blood testing, the officer cannot simply force a blood draw on the spot. The U.S. Supreme Court has held that police generally need a search warrant before they can compel a blood sample after a DWI arrest.

Do not mistake that for a loophole. Texas has built a streamlined warrant process. During "No Refusal" enforcement periods — common in Montgomery County around holidays and special events — judges are on standby around the clock to review warrant applications, and officers can often have a signed warrant in hand electronically within minutes of your refusal. Refusing may delay the draw. It often does not prevent it.

Texas law also makes blood draws mandatory in certain situations, even without a warrant. An officer must take a blood specimen if you are arrested for a DWI-related offense and the officer reasonably believes any of the following:

• A crash occurred in which someone other than you suffered serious bodily injury or death
• A child under 15 was a passenger in your vehicle — see our page on DWI with a child passenger
• You have two or more prior DWI convictions, or a prior conviction for intoxication assault or intoxication manslaughter

Even these mandatory draws are not bulletproof. Texas's highest criminal court has held that a warrantless blood draw taken solely under the mandatory draw law — without a genuine emergency that excuses getting a warrant — can be unconstitutional. Defense attorneys regularly challenge these draws — and the way yours was taken deserves scrutiny.

If officers took your blood after you said no — with a warrant, without one, or under the mandatory draw law — do not assume the result will hold up. Contact our Conroe office and we will examine the warrant, the draw, and the paper trail behind your sample to determine whether that evidence can be kept out of your case.

What the BAC Numbers Mean for Your Charge

Texas law sets several BAC thresholds, and which one applies to you can change the complexion of your case:

• 0.08 is the standard threshold for DWI for drivers 21 and older operating non-commercial vehicles.
• 0.15 or higher elevates a first-offense DWI from a Class B misdemeanor to a Class A misdemeanor — a significantly harsher tier of DWI penalties and fines.
• 0.04 is the standard for commercial drivers while operating a commercial vehicle.
• Any detectable amount of alcohol can mean charges for drivers under 21 under Texas's zero-tolerance policy.

Two things about these numbers cut in opposite directions. First, you can be charged and convicted with a BAC below 0.08 — under the "loss of faculties" definition of intoxication, the state can prosecute you on evidence that you did not have the normal use of your mental or physical faculties because of alcohol, drugs, or a combination of substances. Second, and this is the one to hold onto: a BAC above 0.08 does not convict you by itself. The number still has to survive scrutiny, and that is where your defense begins.

The Mistakes That Hurt You Most After a DWI Arrest

What you do in the hours and days after a DWI arrest can shape your case as much as anything that happened at the stop. These are the mistakes we see most often — and how to avoid them.

Sitting on the 15-day deadline. You have 15 days from your arrest to request an ALR hearing. Miss it, and your license suspension becomes automatic and cannot be contested. This is the single most damaging mistake we see, and it is entirely avoidable — get an attorney involved as soon as possible so the request is filed on time.

Treating the test number as a verdict. A result above 0.08 is not a conviction. Breath and blood tests can be challenged on many grounds, including procedural violations, equipment issues, chain of custody problems, and the scientific limitations of the testing methods themselves.

Talking to police about your drinking. Anything you volunteer about what you drank, when, and how much can hand the prosecution statements that strengthen their case. You have the right to remain silent after your arrest. Using it does not make you look guilty — it protects you.

Staying quiet about your medications. Prescription medications and other substances can affect how you perform on field sobriety tests and what shows up in a blood sample. Your attorney needs the full picture to build an effective defense, so do not hold that information back.

How We Challenge Breath and Blood Tests

The first thing we do when a case turns on a chemical test is demand the records behind the number. At Griffin & Cain, our approach is detailed and evidence-driven:

• Challenging the legality of the traffic stop and the arrest that led to the test
• Requesting calibration, maintenance, and certification records for the breath testing equipment
• Examining whether the blood draw complied with Texas law's strict rules on who may draw blood and how samples must be handled
• Reviewing chain of custody documentation for blood samples
• Retaining forensic toxicology experts when the science behind the result is in dispute
• Filing motions to suppress when your constitutional rights were violated during the investigation

Local knowledge sharpens every one of those tools. We have experience with the law enforcement agencies, testing facilities, and prosecutors who handle DWI cases in Montgomery County. That familiarity helps us spot the issues most likely to arise in your case and build a defense strategy around your specific facts — not a template.