Blood testing is often considered the most accurate method for determining a driver’s blood alcohol content (BAC). Many people believe that a blood test cannot be challenged, but this is far from the lawyers that handle traffic tickets While blood tests are more precise than breathalyzers or field sobriety tests, they are still prone to errors, contamination, and procedural mistakes. Understanding how blood tests work—and how they can be questioned—is essential for an effective drunk driving defense.
A blood test involves drawing a sample of the driver’s blood, storing it properly, and sending it to a laboratory for analysis. Each step of this process must follow strict guidelines to ensure accuracy. One key area of scrutiny in a drunk driving defense is the chain of custody. This refers to the documentation showing who handled the blood sample, when it was handled, and how it was stored. If the chain of custody is incomplete or inconsistent, the defense can argue that the sample may have been tampered with or mixed up, making the results unreliable.
Another important area involves procedural errors during the collection process. Blood must be drawn by a qualified individual using sterile equipment and approved techniques. Mistakes such as using alcohol-based swabs, improper needle insertion, or failure to mix preservatives correctly can compromise the sample. If the defense can show that the collection process violated established guidelines, the results may be challenged or dismissed.
Improper storage is also a significant concern. Blood samples typically contain preservatives and anticoagulants to prevent fermentation and clotting. If the sample is stored at the wrong temperature or for too long before testing, fermentation may occur, causing alcohol levels to rise artificially. Likewise, incorrect handling during transport can affect the integrity of the specimen. Defense attorneys often request storage and transport records to identify any mishandling.
The laboratory testing process itself can introduce errors. Laboratories must follow precise procedures when analyzing blood samples, and any deviation can lead to inaccurate results. Issues such as contamination, uncalibrated instruments, or human error during analysis can compromise the final BAC reading. Defense attorneys may hire independent experts to review lab procedures or conduct retesting of the sample to verify accuracy.
Another critical component of blood test defense is the timing of the blood draw. Alcohol absorption varies based on food intake, metabolism, and drinking patterns. If there was a significant delay between the traffic stop and the blood draw—sometimes an hour or more—the BAC at the time of testing may not accurately reflect the driver’s BAC at the time of driving. This is known as the rising blood alcohol defense, and it is commonly used when the timing of the test is questionable.
Additionally, medical conditions can influence BAC readings. Certain metabolic disorders or medications can affect how the body absorbs and eliminates alcohol. If these factors were present during the test, the defense may argue that the BAC result does not truly reflect impairment.
Ultimately, while blood tests are powerful tools in drunk driving cases, they are not immune to doubt. A thorough analysis of the collection, storage, and testing processes can reveal weaknesses that significantly impact the prosecution’s case. Understanding these vulnerabilities allows individuals to build a stronger drunk driving defense and improves their chances of achieving a favorable outcome.