What You Need To Know About The Accuracy Of DUI Blood And Breath Testing

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What You Need To Know About The Accuracy Of DUI Blood And Breath Testing

13 January 2019
 Categories: Law, Blog


Blood and breath tests are commonly used to determine if a driver has a blood alcohol concentration (BAC) that exceeds the legal limit. Drivers who exceed this limit, which is 0.08% in most states, can be charged with driving under the influence (DUI) or driving while intoxicated (DWI), leading to jail time, fines, loss of driving privileges and other penalties. Although driving under the influence is a dangerous practice, the blood and breath tests used to determine a person's BAC level are not always accurate. Anyone charged with driving under the influence should contact a DUI attorney immediately. 

The Role of Human Error

Even if the machines used to test blood and breath samples work properly, they are still operated by humans, making human error a possibility. When administering a breath test, a police officer must follow a set of standards that reduce the risk of sample contamination. For example, the officer is supposed to observe the driver for approximately 20 minutes before administering the test. Blood, vomit and other fluids can influence the results of a breath test, so this observation period is used to ensure that the test is as accurate as possible. Unfortunately, police officers receive many calls during their shifts, and they may not want to wait a full 20 minutes before giving the test. Administering the test too early can lead to inaccurate results.

Human error also plays a role in the collection and analysis of blood samples. Law-enforcement professionals are required to maintain the chain of custody for each sample, which means they are supposed to document the name of each person who handled the sample and account for the whereabouts of the sample from the time it was collected until the time laboratory personnel finished analyzing it. If the chain of custody is not maintained, a DWI defense attorney is likely to argue that the results should not be admissible in court. Human error also comes into play when laboratory personnel mishandle blood samples or use equipment that has not been calibrated correctly.

Environmental Factors

Many environmental factors also affect the accuracy of blood and breath tests. Depending on the type of device used to collect the sample, the presence of varnish, paint fumes and other chemicals can alter the results of DUI breath tests. For blood tests, the sample must be drawn in a sterile environment, mixed with the right amount of preservative, and stored at the right temperature. If the sample is not collected, preserved and stored properly, bacterial growth could alter the BAC result by producing ethanol, a type of alcohol.

Medical Conditions

People with certain medical conditions have a higher risk of receiving inaccurate results on a breath test, as some medical conditions produce chemicals that are similar in composition to the ones found in alcoholic beverages. In someone with acid reflux, a condition that causes stomach acid to back up into the esophagus, a breath sample may contain chemicals from the stomach. The breath test is supposed to be performed only on a sample from the lungs. In a person with diabetes, acetone gives the breath a fruity smell, and a breath-testing device may mistake the acetone for alcohol.

The penalties for a DUI conviction are severe, especially for someone who has a previous conviction for the same crime. That is why it is so important to make sure the results of any blood or breath tests are accurate. A DUI defense attorney, such as Kevin T Conway Esq Pc, can raise issues such as human error, environmental contamination and medical conditions during the trial.