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Busting the Myth of the “Infallibility” of Blood Testing

By Craig Rosenstein

Craig J. Rosenstein represents clients in many aspects of criminal law, including misdemeanor and felony cases, with a focus on driving under the influence (DUI) defense. He graduated from the University of Arizona in Tucson, Arizona where he received his Bachelor of Arts degree in political science and then attended Arizona State University where he received his Juris Doctorate (J.D.) degree. He is licensed to practice law in Arizona, as well as in the U.S. Federal District Court in the District of Arizona. He can be reached by phone at (480) 248-7666 or you can fill out our convenient online contact form below.

As criminal defense attorneys, we often hear from our clients that they were advised by their non-criminal attorney friends or acquaintances that since they had taken a blood test subsequent to an arrest for DUI, it is pointless to even bother fighting their DUI charge. This attitude stems from the misconception that the state’s blood tests are somehow infallible. That rumor is simply incorrect. This fallacy, in part, stems from a culture inundated with crime-solving TV shows where once blood is discovered at the scene and tested by a forensic scientist in the lab, the prosecution and police have a slam-dunk case. However, the way blood is actually tested for a blood alcohol concentration (BAC) in Arizona is more akin to mass farming rather than any specialized and detailed process portrayed on a network TV show. The purpose of this brief article is to give a summary of the blood testing process educating the legal community about the imperfections in the state’s testing procedures. Hopefully, this will lead to a change in the mindset about BAC testing, from one of “flawlessness,” to one of inaccuracy fraught with the potential for human and technological error. Further, as a result of those flaws, the process is both ripe and deserving of challenges.

The underlying theme here is that the testing procedures used in order to convict someone of a DUI and thereby subject them to days, weeks, and potentially months of their life in jail or even prison, is in no way an individualized process. In every criminal lab in Arizona, the blood kits (the storage boxes that contain the blood tubes of defendants) are removed from a refrigerator after being transported to the crime laboratory. Usually, about 40 or more defendants’ kits are analyzed at the same time. All of these kits are taken to the lab technician’s cubicle. There, each kit is supposed to be examined and documented. Afterward, one tube of blood is removed from the kit and set aside for testing, as each kit is supposed to contain two tubes of blood from the same person. The blood is then hypothetically allowed to come to room temperature; failure to do so could cause the defendant’s blood result to be reported as significantly higher than the actual reading should be. However, no thermometer is placed into the tubes to test the temperature before the actual testing in the machine is conducted. The lab tech then pipettes a very small amount of blood, usually about a quarter of a drop, through something that, to put it simplistically, looks like a very strange turkey baster. This tiny amount of blood is transferred to another vial that contains a very specific amount of a liquid chemical. This is the vial that is actually run through the machine. The whole accuracy of the testing procedure relies on the fact that every blood tube starts out with the same ratio of blood to liquid chemical in that vial. If the perfect amount of blood is not transferred, then again a person’s blood result could come back artificially inflated. This pipetting is done in repetition throughout the test, about 100 different times, increasing the possibility for error.

Next, the vials to be tested are loaded by hand into the actual testing machine, called a gas chromatograph. The vials are put into a line on a carousel, and each vial is given an identifying number in the machine that correlates them to a specific defendant. Ideally, when the technician gets the printout of the blood readings after all the samples are run, they know that vial number “X” in the machine is actually “Mr. NoName” from Scottsdale. Here it is crucially important that the lab technician loads the vials in the correct spot in the line of cases because if any one vial is loaded out of order, the machine will correlate a blood result with the wrong person.

After the vials are loaded onto the conveyor belt, the machine is turned on. Each vial needs to be warmed to the exact same temperature, as any variations can cause inflated results. The machine then moves the conveyor belt, and one-by-one the vials are punctured by a needle (the same needle for every vial), and the air above the blood in the vial is sucked out. This air is the substance that is actually tested for blood alcohol concentration, not the blood. (Ironic, as the DUI statute proscribes blood alcohol concentrations, not air-above-the-blood alcohol concentrations.) This air testing method is used in contrast to actually testing the blood itself because if a liquid solution was tested, the machine would need to be cleaned in-between each vial to prevent contamination. Clearly, this would cause more work (too much work in the state’s eyes) and would require additional machines and technicians to handle the same quantity of cases. Thus, in contrast to popular belief, the blood of a defendant in Arizona is actually not being tested, instead only the air above the blood.

Further, in many circumstances, the machines themselves have significant software problems that cause incorrect data to be reported. Unfortunately, with budgets being slashed across the state, many jurisdictions are unable to purchase newer machines with upgraded software and technology that may fix some of the problems and bugs that infect the older machines in use. Additionally, the testing in the chromatograph is usually conducted overnight, and the lab technicians aren’t there watching over the process to ensure that no problems occur. The lack of human oversight in machines with known software errors is another major source of concern regarding the accuracy of a defendant’s blood alcohol concentration.

Thus, as one can see, this simplified explanation of the testing process underscores how reliant the blood testing process is on humans. These procedures assume that humans aren’t making errors; in reality, we know that everyone makes mistakes, and the only question is how often. Additionally, the use of older or broken machines is itself cause for concern when discussing the accuracy of reported results. Remember a BAC of .080 results in a guilty verdict, one with .079 results in a not guilty one. Minor differences matter. Thus, it is up to criminal defense attorneys to expose the flaws in the blood testing process, and continue to fight against the unjustified and patently false assumption that blood tests are always accurate and therefore useless to challenge. It is the duty and responsibility of every single criminal defense attorney to make the state prove every element, of every crime, beyond a reasonable doubt. The state’s testing procedures in general provide a multitude of reasons to doubt the accuracy of a reported blood alcohol concentration. These tests results are anything but infallible and should be zealously and whole-heartedly challenged.

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