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  • Writer's pictureJustin Sparks

Getting a DWI Blood Test After 2 Hours in Texas | Key Details to Consider

As a motor vehicle driver in Texas, it is important to understand the accuracy, reliability, and procedures of a DWI blood test. The results of a Blood Alcohol Concentration (BAC) test are based on the accuracy and reliability of the methods by which the blood sample is collected and stored, as well as the procedures employed in developing the results.

At its highest level, Texas considers a BAC of 0.08% or higher as the legal limit for intoxicated driving. Learn more about DWI blood test levels in Texas. While the law enforcement officer can subpoena a blood sample for alcohol testing, they'll generally start with a breath test. Still, the Supreme Court of Texas does allow for an arresting officer to do a more reliable blood test if they suspect impairment.

What Is the Legal Limit on the Blood Alcohol Concentration in Texas?

What Is the Legal Limit on the Blood Alcohol Concentration in Texas?

In Texas, the legal limit for driving while intoxicated is 0.08%; this means that if a chemical test reveals a blood alcohol concentration (BAC) to be at or above 0.08%, it results in a DWI charge.

To aid in enforcing this law, Texans must provide a breath or blood sample for a chemical test. If a DWI suspect refuses the test, they may face additional charges or have their driver's license suspended for 180 days.

In practice, most arresting officers will wait two hours after the defendant has been arrested before they decide to do a blood draw. This is due to the fact that it takes some time for alcohol to be absorbed into the bloodstream and be detectable via a DUI blood test.

Avoiding a DUI Blood Test

In Texas, an individual has the right to refuse a breath or blood test for DUI charges at a traffic stop. However, if a person does not take a breath test and more than two hours have elapsed since driving, the law enforcement officer could obtain a warrant to draw a sample of the driver's blood and send it for chemical testing. On top of that, not being willing to do either of the tests can result in license suspension for 180 days or more, as the court determines.

This is where a DUI blood test can come into play and be an efficient way of proving the BAC level of the driver at the time of the incident. Blood tests generally disclose more information than breath tests because it measures the actual amount of alcohol in the bloodstream. These results can be submitted in a court of law to establish a legal defense against DUI charges and DUI cases, if necessary.

How Accurate Is a Breath Test?

When attempting to establish an individual's potential intoxication, many people worry about how reliable breath tests can be.

Under certain circumstances, the results of a breathalyzer test can be challenged. However, it is important to know that, given the right conditions, a breath test can be very reliable for determining blood alcohol content (BAC) and overall impairment.

Having blood tests done in addition to a breath test for DUI testing can result in highly accurate results. Despite this fact, it is important to understand that a DUI blood test can be delayed and even compromised due to various circumstances. It is important not to misrepresent or tamper with any blood test results, as it is considered a serious offense.

Are DUI Blood Tests Reliable?

The technology used to conduct blood alcohol tests and measure blood alcohol content has improved by leaps and bounds in the last few years, and the testing accuracy is now quite high. On top of that, the results of a DUI blood test are often used as evidence in court, as long as a qualified technician is the one who collects and tests the sample for blood alcohol level.

When initially pulled over, an officer may administer a breath test. Should this test come back with a result of more than 0.08%, or should the officer's suspicion be strong enough for reasonable doubt to believe the accused is intoxicated, then a blood test will be demanded.

The pullover will also be registered as a DUI case, with the criminal prosecution seeking blood test results. It is good to know that in Texas, a blood test can only be done at a medical facility or another authorized institute and must be done no later than two hours after the accused is arrested. The timeframe is extremely important to follow, as blood tests conducted after this window of time can be viewed as invalid.

The Causes of Unreliable DUI Blood Tests

The results of a DUI blood test are generally reliable, but the only way to know for sure if the blood test results are accurate is to consider any mitigating circumstances surrounding the blood draw.

Tampering with the evidence in any way in a DUI case is illegal and can result in jail time. Contamination after the blood sample has been collected is also a serious offense. On top of that, mixed-up blood test results in a DUI case will result in the court imposing criminal charges on the medical professional responsible for the blood draw.

Breath Test vs. Blood Sample for DWI Cases – Which Is Better?

A breathalyzer test measures the amount of alcohol in a person's breath. The results from this type of test are usually reliable but can be affected by such factors as mouthwash, breath mints, and even food that is eaten just prior to the test.

Alternatively, a blood test measures the amount of alcohol in an individual's blood. This type of DUI test is more accurate and can determine an exact BAC because the blood is being tested directly after it has passed through a person's system. This is one of the reasons why many people prefer a blood test over a breath test.

Plus, recent advances in testing have made DUI blood tests even more reliable. An Alcohol Swab Mass Spectrometer (ASMS) can detect tiny traces of alcohol from a blood sample. The results from this test are very accurate and are unlikely to be questioned in court.

The question of which test is better largely depends on the individual situation. Blood tests tend to provide more reliable results and require a smaller time investment when compared to breath tests; however, the latter is often cheaper and less intrusive, making it the better alternative in some cases.

Ultimately, the decision should be made with the help of a qualified attorney or medical expert who can assess the individual situation. When it comes to determining alcohol level and proving intoxication, a blood test wins. Blood test results are more precise and can be used as evidence in court.

On the other hand, a breath test can serve as a useful tool for law enforcement and can also be used as an early indication of intoxication, which can help prevent someone from operating a motor vehicle while under the influence.

Getting a False Positive in DUI Cases

Understanding the intricate nuances of DUI law and a DUI blood test is crucial for anyone who has been charged with a "driving under the influence" offense.

Unfortunately, it is becoming increasingly common for a DUI blood test to produce a false positive result, which can lead to a missed opportunity to prove innocence and have the charges dropped. The most common blood alcohol content (BAC) tests include breath, blood, and urine tests.

Blood Test Results

One of the most reliable types of DUI blood tests will involve a medical professional taking a small sample of the blood in an independent laboratory.

Depending on the type of test and the DUI statute the driver is subjected to, the blood sample may be tested to check for various drugs in addition to alcohol. However, the accuracy of this valuable test depends on the blood sample being free of contaminants and free of hidden substances which could produce a false positive result.

Certain medical and physical conditions, as well as medications, can also cause a false positive on a DUI blood test. These can include diabetes, antidepressants, and anti-anxiety medications, as well as antibiotics. Even eating certain foods that contain yeast or grains can interfere with a blood test result.

On top of that, if a sample is tested in a lab where the employees are unskilled, overworked, or understaffed, it can lead to less reliable results.

Breath Test Results

A breath test may be performed by police or other law enforcement officers on the roadside. The breath test determines an individual's alcohol level with the help of a machine developed to detect breath alcohol levels. However, there are circumstances that can lead to a falsely positive result in a breath test, such as having just smoked a cigarette or recently used certain mouthwashes and cough syrups.

Alcohol Swab Results

Another source of a possible false positive result during a DUI stop is the use of a cotton swab, much like the ones commonly used to check for the presence of alcohol on a person's breath. This type of swab test is simpler and less accurate than a full, independent laboratory-based breath test and is more likely to produce false positives.

How to Work Around a False Positive at a DUI Stop

False positives can have serious consequences for drivers, but fortunately, victims don't have to face complex legal situations on their own.

Contact an Attorney

To ensure the accuracy of the DUI blood test results and to protect themselves from unjust punishment, drivers should contact an experienced DUI attorney to discuss the case and to mount a strong defense. With the help of a knowledgeable DUI attorney, defendants can begin to take steps toward protecting their rights and defending their future.

Know Rights

The best dwi lawyers will be able to help plaintiffs better understand the DUI statute, review the evidence, and work with them to build a strong defense for the case. Many DUI attorneys offer free consultations, so this can be a great way to evaluate the evidence personally, identify potential areas for dispute, and protect drivers' rights.

The Steps Taken at a Traffic Stop for DUI Testing

When law enforcement or traffic officer suspects that a motorist may be impaired by alcohol and/or drugs, they are likely to pull the driver over and initiate a traffic stop investigation.

Present Documentation

The officer will likely ask the motorist to provide a driver's license, registration, and proof of insurance before asking the person to step out of the vehicle.

Observe Behavior

Once the driver has exited the motor vehicle, the officer will observe the person's physical movements, slurred speech, impaired vision, and other signs of impairment. The law enforcer will likely conduct a gaze test to see if the person's eyes are moving side to side and also a standalone test to gauge the motorist's ability to maintain balance while standing.

On top of that, the officer may also ask the motorist to walk in a straight line to see if their physical movements and coordination are impaired. Based on their observations, the officer may decide to arrest the driver for DUI based on probable cause.

Submit to a Blood/Breathe Test

Once the driver is taken into custody, the officer will likely ask the accused to submit to a blood test and/or breath test to measure the alcohol level. A refusal of this test can result in anything from the suspension of the driver's motor vehicle license to an arrest if the court determines so. Also, you may also be interested in learning about DWI blood tests at hospitals.

Is a Warrant Required for a DUI Blood Test?

The Supreme Court of Texas made it clear that law enforcement officers' ability to take a blood sample from a DUI suspect requires that a warrant must be obtained unless the person has given his or her consent to the test.

In some states, implied consent laws allow a driver to be subjected to the test without a warrant if they do not explicitly refuse the test. The ruling left open the possibility that a warrantless DUI blood test could be upheld if there is reasonable cause to believe that the driver is legally under the influence of drugs or alcohol.

As a result, for the blood test to be admissible in court without a warrant, police must be able to show probable cause and reasonable suspicion to prove that the driver is under the influence.

In summary, whether the police require a warrant for a blood test largely depends on state laws. However, the U.S. Supreme Court has clarified that a warrant is almost always required. While a driver may not legally refuse a breathalyzer, they do retain the right to refuse a blood test unless their state has an implied consent law.

What Are Implied Consent Laws?

All states have so-called "implied consent laws," which provide that persons who are lawfully arrested for suspected DUI must submit to a chemical test without a warrant. Refusal to cooperate with a test can result in criminal and/or administrative consequences. However, even if implied consent is present, a search warrant is necessary in order to legally follow through with the blood test.

Given the sensitive legal issues surrounding a blood test and the necessity for a search warrant, it is essential to have an attorney knowledgeable in this area. If a warrant has been wrongfully issued or the evidence is deemed to be invalid, an experienced attorney can provide legal counsel and assist in determining the best way to proceed.

A free consultation is a great way to gain a better understanding of the case and to learn more about what legal options may be available.

How a DUI Attorney Can Help Accused Drivers

How a DUI Attorney Can Help Accused Drivers

There's no question that getting pulled over and being asked to draw blood is intimidating, especially when it's the first time being charged with such an offense. However, an experienced attorney can help victims navigate the complex legal waters of a DUI charge and help protect their rights. A driver's refusal of such a test can result in an arrest, as well as potential criminal consequences.

However, it is possible for an attorney to challenge a police officer's probable cause to order a blood test. The court also may claim the chain of custody of the sample or the fermentation process. If the results of the blood test can be successfully challenged, this could mean the evidence used to support a DWI charge could be thrown out of court.

With decades of experience with criminal defense proceedings, a qualified attorney will be able to evaluate and explain the chemical tests with the goal of mitigating potential jail, court fines, driver's license suspensions, and other penalties that often come with a DUI conviction.


A DUI arrest and blood test after two hours can be an overwhelming experience. An experienced attorney can provide the defense strategies to challenge the chemical tests and create reasonable doubt.

Additionally, depending on the circumstances, an attorney may be able to argue that a blood sample was not properly obtained, stored, or analyzed.

No matter what evidence is presented, every driver in Texas who has been arrested for DUI has a right to legal representation. When considering legal counsel, it is important to find someone experienced in DUI cases who will work hard to get the best outcome for their client. The attorneys at Sparks Law Firm offer a free consultation for clients to discuss the specific facts and circumstances of a case.


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