September 11, 2023

Photo of Breathalyzers

Breathalyzers and blood tests both serve the same fundamental purpose: to measure the presence of alcohol in the body. However, these methods employ distinct approaches and come with their own set of limitations and legal implications. 

This breathalyzer vs. blood test comparison discusses these critical aspects, shedding light on the broader legal significance of each testing method. 

Difference Between Breathalyzer vs. Blood Test

The methods used to measure blood alcohol concentration (BAC) play a crucial role in determining the outcome of legal proceedings. 

Here are the differences between a breath test and a blood test: 


A breathalyzer test measures the alcohol content in a person’s breath by analyzing the amount of alcohol vapor present. 

During the test, the individual in question blows into a handheld device filled with potassium dichromate and other chemicals, which are a red-orange color. 

When alcohol is present, the liquid solution changes from red-orange to green. The extent of this color change corresponds to the level of alcohol in the person’s breath. 

Modern breathalyzer devices, like the Intoxilyzer 9000—the only instrument Texas uses for evidential breath alcohol analysis—feature advanced technology like semiconductor sensors or infrared spectroscopy to provide a more accurate BAC reading. 

These devices aren’t influenced by endogenous substances like acetone (produced by diabetics), toluene (produced during petroleum refining operations), and carbon monoxide. 

Blood Test 

Blood tests involve drawing a blood sample from the person by a licensed medical professional. 

The police will transport the suspected individual to the hospital to perform the procedure, per Texas Transportation Code §724.012. The officer will provide the medical staff with the necessary information related to the case, and request for the results when done.

Unlike breathalyzer tests, blood tests don’t offer instantaneous results. After being released from custody, it takes a few days or weeks before the blood results are known.  

Photo of Blood Samples


Compared to blood tests, breathalyzer tests have a 50% margin of error. The accuracy of these tests depends on factors such as the type of breathalyzer used, the calibration of the device, and the specific circumstances of the individual being tested (medication, sex, weight, etc.). 

If you had a drink 15 minutes before the test, for example, trace amounts of alcohol in your mouth could lead to an inaccurate result. Medication and smoking can also affect results, as well as products that contain alcohol like breath fresheners and mouthwash.  

This begs the question, why are breathalyzers still used if they have a 50/50 chance of error? The answer is simple: they’re simpler and less expensive than blood tests. Breathalyzer tests are quick and convenient, providing immediate results on-site. They’re also less invasive. 

Blood tests are considered the gold standard for BAC measurement due to their higher level of accuracy. They can also detect the presence of drugs. 

But since they’re invasive, Texas limits the use of blood tests as a first resort. The officer in charge must first request a breath test or a urine test before requesting a blood sample. 

Legal Implications 

In most cases, breathalyzer tests aren’t admissible in court. They’re simply not accurate enough to determine that the driver was really over the legal limit. 

Poor maintenance, calibration, and improper or untimely administration can all produce false positives, skewing the test results. The police officer can come to court and give their account of what took place, but they can’t use the test results against the driver.

This isn’t the case with blood tests. Blood tests are more reliable in court, and their accuracy is less likely to be contested compared to breathalyzer tests. This means that they can be used as evidence in DUI cases. 

That said, blood tests aren’t bulletproof in court. 

An experienced lawyer might question the validity of the sample, the transportation process, or even the calibration of laboratory equipment. They may also get test results thrown out if police violated the driver’s constitutional protections or did not follow procedural requirements. 

Can You Legally Refuse a Breathalyzer or Blood Test? 

When you obtain a license in Texas, you implicitly agree to give a breath or blood sample when arrested for DWI. 

This legal provision is referred to as the implied consent law, which kicks in after being lawfully arrested for DWI.  

Refusal to take a breathalyzer or blood test can lead to various consequences and penalties, with the most common being the suspension of the driver’s license

The suspension is based on how many offenses the driver has. If it’s the first offense, the license will be suspended for 180 days. If it’s the second, it extends to two years. For the third, the suspension lasts 10 years. 

In Texas, drivers have a right to challenge the suspension 15 days following the arrest. If the driver fails to do so, the Texas Department of Public Safety (TxDPS) will automatically suspend the license for the maximum allowable period. 

Photo of an Angry Man

Can Police Take a Breath or Blood Sample Without Your Consent? 

Police officers can take a breath or blood sample without explicit consent if the police officer believes he has probable cause that your blood contains evidence of a crime. The police officer must apply for a search warrant that contains probable cause that your blood contains evidence of a crime, swear to the affidavit and have a Judge sign the warrant. Once the officer has a signed warrant they can order any qualified person, a phlebotomist, to draw your blood. 

Wrapping Up 

A breathalyzer test involves blowing into a handheld machine to gauge alcohol levels in the driver’s breath, while a blood test involves taking a blood sample to measure alcohol levels against the allowed BAC. 

The former is far less accurate than the latter, with some readings showing significant discrepancies between the two tests. Factors such as medical conditions, residual mouth alcohol, and machine maintenance can lead to inaccurate readings. 

Blood tests are regarded as a more dependable source of evidence in court, and are often given significant weight in DUI cases.

While you’re well within your right to refuse these tests, refusal can lead to the suspension of your driver’s license, fines, and other legal complications. 

If you find yourself in this situation, seeking legal counsel from an experienced Conroe DUI attorney is crucial to navigating the legal process.