Although breath samples are the most common way for law enforcement officials to gauge blood alcohol content (BAC), the authorities may arrange for an actual blood sample. It's one of the most accurate means of determining BAC, but it's also intrusive and somewhat complicated from a legal point of view. The following offers an in-depth explanation of how DWI blood testing works, what to expect and how it may affect the outcome of your DWI case.
When Blood Testing May Be Requested
Upon your arrest for a DWI offense, the arresting officer may request that a blood test be performed to accurately determine your current BAC level. Most states require police officers to obtain a warrant in order to take blood samples from those being charged with DWI offenses. A recent Supreme Court decision affirmed this policy, making it more difficult for law enforcement officers to demand blood testing unless enough probable cause is established to justify a written warrant.
In some states, implied consent laws may require you to submit to a blood test without a warrant. However, refusing to submit to blood testing in these states may cost you your driver's license for a certain length of time. For instance, the state of California may suspend your driver's license for a year or more, depending on how many previous DWI offenses you've committed.
Serum Blood vs. Whole Blood
Blood samples obtained for the sole purpose of determining BAC levels can be analyzed under two different conditions: whole blood and serum blood. The differences between the two are often significant enough to drastically affect the outcome of the DWI case.
Whole blood samples (also known as "legal blood") are samples that retain all of the solid and liquid components that make up human blood. Such samples are often taken at the scene of the accident or point of arrest by nurses or paramedics at the scene. The vast majority of DWI cases that take blood samples into account often rely on whole blood samples.
Serum blood samples (also known as "medical blood") are commonly taken at a hospital by trained, qualified personnel under strict protocol. Unlike whole blood samples, serum blood is processed in a centrifuge that separates the liquid (the serum) and solid portions from one another. Most serum blood tests focus on the liquid portion of the sample.
A major difference between whole blood and serum blood analysis is that BAC levels in the latter can appear as much as 16 percent higher than the former, according to DWI attorney Patrick Mahaney. For this reason, the courts must convert the results of serum blood testing into a whole blood equivalent using a mathematical formula.
The use of serum blood in a DWI case could prove to be the tipping point towards an unfavorable verdict, especially if your BAC level is a mere point under the legal limit according to whole blood tests.
Grounds for Suppression
If your DWI case hinges on blood sample testing, there are plenty of circumstances and factors that could allow your attorney to successfully suppress that piece of evidence:
- Obtaining the sample without a warrant, unless exigent circumstances could be proven to forgo a warrant
- Delays in the testing process and improper storage techniques that result in the sample's fermentation
- Failure to meet basic chain of custody requirements, opening the door for tampering concerns
- Lack of a sworn law enforcement official as a witness to the blood-drawing process
- False positives due to physiology or a legally prescribed medication
Depending on the above circumstances, a diligent defense attorney may be able to question the admissibility of your blood sample in the DWI case, thereby improving your chances of a favorable verdict. For more information, contact a firm like Hornthal Riley Ellis & Maland LLP.