Should You Do a Breath Test or Blood Test on a DWI in San Antonio?

When an officer arrests you for DWI in San Antonio, the officer will ask you if you will do a breath test or blood test. If you refuse to do a breath test, the officer will get a search warrant to draw your blood to have it tested for alcohol or, possibly, for drugs.

What should you do if you’re in this situation, is it better to agree to do a breath or blood test or to refuse and let them get a warrant for a blood test? I say to refuse and let them get a warrant for a blood test.


If you consent to either a blood or breath test, there’s no legal barrier to keeping that sample out of court. When you refuse, the officer has to go to a judge, give the judge an affidavit stating the reasons that he believes that you are intoxicated. If the affidavit states enough facts to show the judge that you are intoxicated, the judge issues a warrant. Any mistakes that the officer or judge make on the affidavit or warrant could result in keeping the blood test results out.

The other analysis that we go through is determining how each test looks at trial. When you provide a consent to a test, you give two samples into the breathalyzer. The two samples rarely have the same BAC (Blood Alcohol Concentration), for a variety of reasons, but mainly because the breath test is more of an estimate. Juries generally believe that breath tests are less reliable than blood tests, because they are less reliable.

With a blood test, a nurse draws your blood, sends the blood to a lab to be analyzed and a technician at the lab tests the blood and comes up with a result about what your BAC is. There have been several issues with blood draws recently. It is still unclear whether a second search warrant needs to be issued to test the blood after it is drawn. There was recently a recall on test tubes that made the results less reliable. There have been problems with different laboratories not following the propert procedures, leading to unreliable results.


The short answer is that there are problems with both the breath test and the blood test. There are reasons for and against each test. Because there’s no longer a clear answer as to which test will benefit you more, I go back to my default answer of refusing to consent to any test or search that the police offer. This works best if you refuse to answer any questions regarding alcohol or drugs and refusing any field sobriety tests. The fewer things the officer can put on his affidavit to get a search warrant, the better chance we have of keeping any breath or blood test out.

If you’ve been arrested for DWI in San Antonio or if you have any questions about whether you should give a breath or blood test, set up a FREE consultation with me so that I can answer your questions.

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Sean Henricksen Law Firm

At the Henricksen Law Firm, we are committed to helping good people who have been charged with criminal offenses. Your situation is unique, and before we develop a strategy, we will hear your individual concerns. Then we work toward the result that solves all of your problems—both now and in the future.

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