When a blood or breath test shows that a driver’s blood alcohol content is above 0.08 percent, many suspects assume that a DUI conviction is inevitable. This is not necessarily the case. Like any technology, blood alcohol tests are not infallible, and there are ways to challenge test results to avoid improper DUI convictions.

The Known Error Rate

Most medical tests have a known error rate, which allows doctors to analyze test results within a given confidence interval. For example, if a test is known to be highly accurate, a doctor will be more likely to start treatment that is recommended by the outcome of that test. If a test is known to be somewhat or not very reliable, a doctor is more likely to corroborate the test’s findings with other examinations.

In the case of blood, breath, and urine samples, medical science has been able to determine a fairly accurate confidence interval. Numbers vary, but prosecutors and defense attorneys can still use that range to determine the likelihood that a particular defendant’s blood alcohol test was accurate.

For example, if a defendant’s breath test showed a blood alcohol content (BAC) of 0.081 percent, a prosecutor would consider the accuracy of breath tests. If breath tests are generally about 90 percent accurate, the defendant’s actual BAC could fall anywhere from 0.073 percent to 0.088 percent. The defense attorney can then use this knowledge to advocate for the defendant. In this situation, many prosecutors will agree to a plea deal for a lesser charge, such as reckless driving. If the prosecutor refuses to do so, the defense attorney can take the case to trial, if necessary, and present the jury with evidence of the known error rate of blood tests. The jury then has reasonable doubt that the defendant’s blood alcohol content was, in fact, at or greater than 0.08 percent.

Regular Maintenance and Proper Functioning

In other cases, defense attorneys are able to challenge the findings of a breath test with far less technical arguments. Breathalyzers require regular inspections, tests, and maintenance by the law enforcement agencies that use them. These agencies maintain records about the inspection and maintenance of their breath testing equipment. If a machine has malfunctioned in the past or has not been maintained in accordance with the manufacturer’s specifications, it may not yield accurate test results. This, too, is a finding that can be used to either negotiate an appropriate deal with the prosecutor or introduce reasonable doubt to the jury at a trial.

Blood tests must also be conducted according to protocols. Technicians must be trained in appropriate law enforcement collection techniques (which can differ from medical techniques). A chain of custody for the blood sample must also be established, which ensures that the specimen is accounted for at all times to preclude tampering with the evidence. These and other considerations can introduce reasonable doubt to a jury considering the accuracy of a blood sample.

West Chester DUI Defense Attorney

Experienced Pennsylvania DUI defense attorney Michael J. Skinner is a former prosecutor—and by knowing how to present a case to the prosecution, he is able to advocate effectively for his DUI clients. He also protects their important constitutional rights, so please call the Skinner Law Firm at (610) 436-1410 today to schedule your free consultation.

Article Author

Michael J. Skinner, the founder of Skinner Law Firm LLC, is a former prosecutor with the Chester County District Attorney’s Office.

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