What Is the Difference Between a Breath Test and a Blood Test?

 What Is the Difference Between a Breath Test and a Blood Test?

If the police ever pull you over for a DUI, you may wonder what test the officer will give you. It’s no secret that law enforcement officials use a variety of methods to determine whether a driver is under the influence of alcohol  or not. 

So, you may be wondering what kind of test the officer will give you. Well, law enforcement officers use two types of tests to check the state of drivers: a breath test and a blood test.

So, what is the difference between the two types of tests? And which one is more accurate?

This blog post offers key insight into both types of tests. It breaks down the differences between these two types of tests and helps you know which one to expect if you’re stopped for a DUI. We will also talk about  which of the two tests police officers prefer and why. 

Let’s get started!

Breathalyzer vs Blood Test

A breath analyzer (also known as a breathalyzer) is a device used to estimate blood alcohol content (BAC) from a breath sample. The test works by having the suspect blow into a tube attached to the device. Breathalyzer tests are quick and easy to administer. Still, their accuracy level is something that people tend to question pretty often. That coffee and other food in your mouth will affect the accuracy of the result. Likewise, mouthwashes and other substances can skew the results of a breathalyzer test.

Other factors may also affect the accuracy of results obtained by the breathalyzer. For example, the type of device used influences the results’ accuracy. Likewise, the device’s calibration and method of use play key roles.

In contrast, a blood test measures the amount of alcohol present in the blood.  While blood tests are more accurate than breathalyzers, they are also more invasive.  As such, law enforcement officers enlist the help of a trained medical professional. They collect the blood sample, which the officer then takes to the crime lab for analysis. 

In general, breathalyzer tests are good for screening purposes.  Blood tests are better for confirmatory testing. If there is any doubt about the results of a breathalyzer test, a blood test becomes the next best thing.

While the police don’t need search warrants to get a breath sample, they do for blood samples. This rule is in accordance with the United States Supreme Court. It states that police officers must have a search warrant before vying for a chemical test. 

Nonetheless , the Supreme Court makes provision for police officers to gather blood samples. The rules state that they can gather blood samples if the  driver in question is unconscious.  However, they must only do so if they cannot administer the standard evidentiary breath test. 

What Method Do Police Prefer

In some cases, law enforcement officers may choose to administer a breathalyzer test rather than a blood test when investigating an accident-involved driver.

The advantage of the breathalyzer test over the blood test is that the results are generally available much more quickly. This allows law enforcement to determine the level of impairment and whether the accident was caused by alcohol consumption without significant delay. 

Nevertheless, they can use both tests in court to prove various levels of intoxication, so both remain viable tools in accident-related cases.

What to Do?

You must remain calm if you get stopped because of a DUI suspicion. Remember, the law is on your side as long as you’re not an offender.  If you think the test results gotten are inaccurate, you need to hire DWI lawyers. Even if convicted, having one will prove very helpful. 

For starters, DWI lawyers know how to challenge the results of sobriety tests.  As such, they can help you get approval for an independent test.  

In contrast, if the tests are positive, a DWI lawyer knows how best to fight and build a strong defense on your behalf. An experienced DWI lawyer is familiar with the laws surrounding drunk driving.  Hence, they can provide invaluable guidance throughout the legal process.

Additionally, if you get into an accident with a commercial vehicle, a DWI lawyer can help you navigate the legal process and protect your interests. 

Your DWI lawyer may be able to negotiate a plea bargain with the prosecutor. This gives you the opportunity to gain a more lenient sentence. In some cases, DWI lawyers may even be able to get the charges against you dropped altogether.

Can You Refuse a Breath Test?

In most states, it is completely legal to refuse a breath test. Still, drivers are under the implied consent laws issued by states. According to these laws, drivers arrested on account of a DUI can’t refuse BAC testing. But these provisions come with consequences too. 

In some states, refusing a breath test results in a driver’s license suspension.  Likewise, the police may claim, in court, that refusal means being guilty of a DUI. 

Refusal may lead to a longer suspension period than that of those who do not refuse and have their blood alcohol content above the legal limit. You also risk the installation of an ignition interlock device (IID).

If you are an accident-struck driver and the police believe alcohol is a factor, they may ask for a blood test. Refusing a blood test when a warrant exists can lead to criminal charges.  Some states criminalize refusing to take a test. In such cases, you may face fines as well as jail time if convicted! 

In short, while you can refuse a breath test, it is important to know the potential consequences before making a decision.

Once again, if that is the case, hiring a DWI lawyer is your best chance of fighting the charge.  


You may have to submit to a breath or blood test if caught driving under the influence. While you can refuse the non-invasive breath test, it doesn’t go as well with the blood test. It is even more taxing if the prosecution has a warrant. Still, both have their fair share of hurdles.

If you face charges after either type of sobriety test, it’s important to consult with an experienced DWI lawyer. An experienced DWI lawyer can help you fight the charges and protect your rights.

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