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Arizona DUI Defense – Blood Test Inaccuracies for 2021

How to Defend against a DUI Charge in Arizona:  5 Ways Blood Tests Can Be Inaccurate

In Arizona, drivers may be charged with a DUI if their blood alcohol content is 0.08% or higher. Blood tests are widely accepted as being the most accurate way of determining blood alcohol concentration in drivers suspected of DUIs and are often the only objective evidence of a defendant’s guilt, making the validity of the test a central question in a DUI trial.

According to Stanford University, the effects of BAC levels can vary from person to person, male or female, slender or heavier; even medication can play a significant role on the blood alcohol readings. Stanford has published a BAC Graph showing the levels of blood alcohol.

Contrary to popular belief, blood tests are not always conclusive in proving that a driver’s blood alcohol content was above the legal limit. As explained below, many factors affect the accuracy of blood test results.

If your case involved the taking of blood or urine during your DUI arrest, you will need to wait and see if your BAC results come back at a reading of .08% or greater. This process can take between one (1) and six (6) months for your results to return. In the event your BAC readings are above a .08% the officer will send a suspension of driving privileges to the Arizona MVD office. You will then be notified with a “Corrective Action Notice” (i.e., notice of suspension). As soon as you receive this from the DMV, speak to our certified Phoenix DUI Specialist immediately so we can start the DUI Defense process and request a hearing on your behalf. This hearing request needs to be done within fifteen (15) days of the date of that suspension notice.

How can blood alcohol test results be challenged?

Below are 5 common categories of problems that may lead to the dismissal of DUI charges against defendants who have undergone blood alcohol testing:

  1. Problems with storage of samples

Storage issues are a common reason for inaccurate blood test results. After a blood sample is collected, it is stored in a vacutainer, a vacuum-sealed test tube designed to prevent contamination of the blood samples. Vacutainers contain certain chemicals that prevent bacterial contamination and prevent the blood from clotting, including sodium fluoride and potassium oxalate.

Errors related to the proper handling of the vacutainers and their contents can skew the results of blood tests. For instance, the seals on vacutainers have a specific expiration date beyond which the containers can no longer be considered to be reliable for preventing contamination errors. However, lab technicians who perform a large number of testing often forget to check the expiration dates on the vacutainers.

Further, if the seal on the vacutainer it broken, it can affect the amount of chemicals inside the vacutainers. If there the vacutainer contains insufficient amounts of sodium fluoride, the blood sample may be contaminated with bacteria that may promote fermentation in the vial that leads to higher blood alcohol content results than were actually present at the time the sample was collected. Insufficient levels of potassium oxalate may allow the blood sample to clot, which artificially raises the blood alcohol levels due to altered ratio of liquid to solids.

  1. Problems with hospital lab testing

In cases where a defendant has had his blood alcohol tested in a hospital, as in the case of a serious auto accident, sometimes the prosecution may rely on hospital lab testing instead of sending a sample to a forensic lab. Blood testing performed in a hospital is conducted for medical purposes, while testing conducted in forensic labs are performed with the purpose of determining whether a crime has been committed. Thus, forensic labs must follow certain safeguards that prove a defendant’s guilt beyond a reasonable doubt that are irrelevant for the purposes of medical treatment.

For instance, forensic labs test a whole blood sample when determining blood alcohol content. However, hospitals typical only test the blood plasma, the portion of blood left over after the liquid has been removed. The difference in technique is significant because alcohol is more concentrated in the serum and thus the blood alcohol content will higher than it would be if the whole blood sample were tested.

Further, certain injuries from a serious automobile accident and high BAC cause muscles and organs to produce lactic acid. Blood alcohol tests cannot distinguish between ethyl alcohol and lactic acid, leading blood tests at hospitals to be much higher than they were at the time the defendant was driving.

Moreover, in many cases, the testing kits used by hospital contain instructions that specify that the test kits are not designed for forensic purposes. At a minimum, the prosecution should be required to call an expert to explain the hospital blood tests and any potential discrepancies between the hospital’s testing and the defendant’s actual blood alcohol content at the time the blood was drawn. The expert will also need to address other differences in hospital testing procedures from forensic laboratories, such as the collection of arterial blood instead of blood from the veins for testing purpose and any use of alcohol swabs at the injection site that may affect the blood alcohol test results.

  1. Problems with collection of the blood sample

Issues with collection of the blood sample present another major area that affect the validity of blood test results. The technicians who draw the blood often only have minimal training in collection procedures and make mistakes that can significantly alter the results. For instance, if technicians use swabs containing alcohol to clean the injection site, the blood test results may be higher than would ordinarily be. Many other problems with collection of the sample can also invalidate the result, such as failing to properly prepare the injection site and collecting a sample that is too small or large.

  1. Problems with procedures

In proving a DUI case, the prosecution has the burden of establishing a chain of custody of the blood sample in order for the results of blood testing to be admitted into evidence. The prosecution must account for the sample at all times from the time the sample is collected to the time the results of the testing are recorded, and records must be kept of when the sample has changed hands and the time and date of the transfer.

In order to admit blood testing results into evidence, the state must establish facts such as the:

  • identity and qualifications of the person who collected the blood sample;
  • identity and qualifications of laboratory technician who analyzed the sample;
  • time, date, location and circumstances under which the sample was collected;
  • calibration and maintenance records of the equipment used to test the sample;
  • suitability of the method of testing the sample;

Any discrepancy or omission in chain of custody evidence may lead the judge to determine that the state’s blood alcohol testing should be inadmissible and make dismissal of the DUI charges against the defendant more likely.

  1. Laboratory and Equipment Errors

Many forensic labs are poorly funded and staffed and are subject to little or weak oversight from outside agencies. Improper maintenance of the equipment used to test the blood samples may have caused errors in the result. Further exacerbating the problem are that most forensic labs are closely aligned with law enforcement and thus may be unduly influenced to produce results that lead to convictions. In some instances, lab technicians have even been found to have intentionally altered results used in convictions of criminal defendants.

In Arizona, within 60 days of the testing, defendants charged with DUI have the right to request a sample of the blood tested by the state so that it can be independently tested at a private laboratory of the defendant’s choosing. Often, the results of the independent testing reflect a significantly lower blood alcohol content than the testing by the state revealed. This discrepancy can be helpful in questioning the accuracy of the state’s blood testing and may assist in getting an acquittal or the DUI charges dropped.


Many defendants who have been charged with DUI based on the results of blood testing mistakenly believe there is no hope to defend against the charges against them. However, the state has a high burden of proof in criminal cases, and, as explained above, there are many potential areas where the prosecution’s blood alcohol testing can be challenged. Thus, if you have been arrested for DUI, you should contact an experienced dui defense attorney right away.

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