Driving under the influence of alcohol or drugs is illegal in every state. And all states have “implied consent” laws that require drivers to take a chemical test (usually, of the blood, breath, or urine) if lawfully arrested for driving under the influence (DUI).
This article covers DUI blood testing—specifically, when drivers must agree to take a blood test and how prosecutors use blood test results in DUI cases.
Purpose of DUI Chemical Testing
The chemical tests officers use in DUI cases generally involve taking samples of the driver’s blood, breath, or urine. The purpose of these tests is to determine whether the driver has any alcohol or drugs in his or her system. Prosecutors can use the results of these tests to prove the driver was under the influence or had an unlawful concentration of alcohol or drugs in his or her body.
Advantages of Blood Testing From the Prosecution’s Point of View
For law enforcement and prosecutors, blood tests are generally preferable to breath or urine tests. Blood test results are more reliable than other types of tests because they give a direct measurement of the amount of alcohol in the driver’s system. Law enforcement sometimes prefers blood tests because, in addition to alcohol, they also detect drugs in the driver’s system.
When an Officer Can Lawfully Require a Driver to Take a Blood Test
To lawfully obtain a blood sample from a driver, the officer must have:
- the driver’s consent
- a warrant issued by a judge, or
- “exigent circumstances.”
However, these circumstances require a bit more explanation.
What it Means to “Consent” to a Blood Test
All states have “implied consent” laws that require drivers lawfully arrested for a DUI to submit to chemical testing if asked to do so by an officer. Drivers who refuse generally face license suspension or revocation. So, while drivers can refuse to consent to a blood test, doing so usually comes with consequences.
Warrants for Blood Tests in DUI Cases
Search warrants are another way an officer can obtain a blood sample from a driver. If the driver is unable or refuses to consent to a blood test, the officer can ask a magistrate or judge for a search warrant to obtain a blood sample. To obtain a warrant, the officer must show there’s probable cause to believe the driver was violating the state’s DUI laws.
When “Exigent Circumstances” Might Justify Taking a Blood Sample From a Driver
In some situations, exigent circumstances might allow an officer to obtain a blood sample without consent or a search warrant. Basically, exigent circumstances exist if a reasonable person would believe that quick action is necessary to prevent the destruction of evidence. In other words, there’s no time to get a warrant.
Officers are often reluctant to rely on exigent circumstances to justify taking a blood sample from a suspect because of the legalities. Because the exigent circumstances explanation doesn’t always hold up in court, obtaining consent or a warrant is usually a better way to go.
Procedures for DUI Blood Testing
Generally, states have laws specifying how and by whom a blood test should be performed. But, although there are general trends, the details of state law requirements certainly differ.
Where DUI Blood Testing Takes Place
Since a blood test is a medical procedure, officers typically transport drivers to a hospital for the test. However, in some instances, a blood test might take place in some other location such as a police station or a DUI checkpoint. The main issue with location is there needs to be a qualified person there available to draw the driver’s blood under sanitary conditions.
Persons Authorized to Perform a Blood Draw on a DUI Suspect
Doctors, nurses, emergency medical technicians (EMTs), and phlebotomists are medical personnel most states authorize to draw blood for chemical testing. In addition, some states allow medical personnel not listed in their statutes to draw blood if the prosecution can show the person who drew the blood sample was qualified to do so.
How the Processing of a DUI Blood Sample Works
Many law enforcement agencies provide standardized blood testing kits to the person drawing the blood. These kits might include test tubes to store the blood and instructions for obtaining blood samples.
Following the blood draw, law enforcement will typically seal the package and send the sample to a lab for testing. The testing takes time, and the results might not be available for weeks. The type of testing required and the caseload of the lab performing the testing can increase the time it takes to get results.
Once available, the lab generally forwards the results to law enforcement or the local prosecutor.
Challenging DUI Blood Test Results
Blood test results often provide the most damning evidence against drivers in DUI cases. In all states, a driver can be convicted of a DUI based solely on blood alcohol concentration (BAC). In other words, the prosecution doesn’t need to prove actual driver impairment—only that the driver’s BAC was above the legal limit.
All states have what are often called “per se” DUI laws that make it illegal to drive with a BAC of .08% or more (.05% or more in Utah). Some states also have per se drug DUI laws that make it illegal to drive with a certain concentration of specific drugs in your system.
So blood test results that reveal an illegal concentration of drugs or alcohol can make it easy for a prosecutor to prove a DUI charge. However, defense attorneys have ways of challenging blood test results in court.
Fighting a DUI Charge With a “Rising Blood Alcohol” Defense
Since the body doesn’t absorb or process consumed alcohol all at once, BAC gradually rises and falls. If a driver was drinking shortly before driving, his or her BAC could be in the process of rising when the DUI stop takes place. The rising alcohol defense involves arguing that while a driver’s BAC may have been over the legal limit at the time of testing, it was not over the limit when the actual driving occurred.
However, this defense doesn’t work in all states. In some states, prosecutors don’t need to prove the driver had an unlawful BAC when the actual driving occurred. For example, many states make it illegal to have an unlawful BAC within two hours of driving. These kinds of laws effectively eliminate the rising blood alcohol defense. Police just need to make sure the blood draw occurs within the two-hour (or whatever the time period is) window.
DUI Defenses Related to Problems with the Blood Draw Procedures
Medical personnel must follow the proper procedures when drawing blood from a driver. Otherwise, the sample may be unfit for accurate testing.
For example, clotting can occur when smaller needles are used to draw blood. Clotting elevates the alcohol content in a blood sample because it changes the ratio of liquid to solid, ultimately resulting in unreliable test results.
Also, fermentation can occur when the blood is not properly mixed with the coagulant and preservative in the test tubes or is otherwise stored improperly. Fermentation increases the alcohol concentration of the sample and can lead to an inaccurate test result.
By pointing out lapses in proper procedure, an experienced DUI attorney might be able to cast doubt on the reliability of blood test results.
When Officers Fail to Preserve a Second Blood Sample for the Driver to Test
Some states require officers to obtain two blood samples from the driver: one for the prosecution and one for the driver. Other states require the officer to obtain a second sample only if the driver requests it. If the driver requests that the sample be preserved for additional testing and the officer fails to do so, the court may throw out the results of the blood test.
Problems with Chain of Custody
The blood test result may be undermined by “chain of custody” issues. The officer must make sure that the identity and integrity of the sample are maintained throughout the testing process. If the officer cannot prove to whom the sample belonged and who had possession of the sample during the process, the judge might say they’re inadmissible as evidence in court.
Talk to a DUI Attorney
DUI law is a complicated area of law. And if the prosecution has blood test results, the case against the driver may turn on whether the defense can keep the results out of evidence. An experienced attorney can evaluate the case and determine whether valid grounds exist to attack the blood test.