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Retrograde Extrapolation in a Nevada DUI Case

If your DUI case in Las Vegas, Clark County, Nevada, involves a breath or blood alcohol concentration, your attorney should be familiar with retrograde extrapolation.

Retrograde Extrapolation is defined as a scientific theory that helps the jury estimate what the driver's breath or blood alcohol concentration might have been at the time of driving. Because the evidentiary breath or blood test is rarely taken at the scene immediately after the arrest, a delay always occurs between the time of testing and the time of driving. In the vast majority of these DUI cases, the chemical test occurs more than one hour later at the police station. 

Even if the test was over the legal limit, your criminal defense attorney might be able to use these arguments to convince the jury that at the time of driving the person accused was not over the legal limit of .08. Retrograde extrapolation is a mathematical calculation used to estimate a person's blood alcohol level at a particular point in time by working backward from the time the breath or blood sample was taken by law enforcement after the arrest. Many courts have found that retrograde extrapolation enjoys a general acceptance in the scientific community.

The courts in Nevada have concluded that retrograde extrapolation evidence has some relevance to help the jury determine whether the person was driving under the influence or had a blood alcohol concentration above the legal limit at the time he or she was driving.

Either the state or the defense can present expert testimony on retrograde extrapolation. Therefore, if your case involves a breath or blood alcohol concentration reading, you should seek out the services of an attorney experienced with the scientific theories surrounding alcohol testing including retrograde extrapolation. At Gallo Law Office, James C. Gallo is experienced in fighting DUI cases that involve a BAC reading in a breath or blood test.

Whether your DUI arrest occurred in the City of Las Vegas, the City of North Las Vegas, the City of Henderson or the Clark County Township, James C. Gallo can help you fight the charges. Call (702) 385-3131 today for a free consultation.

Calculations in Retrograde Extrapolation in DUI Cases

The calculation requires information regarding the rates at which alcohol is absorbed and excreted. The rates of absorption and excretion vary based on a number of factors, including:

  • the amount of time between a person's last drink and the blood test;
  • the amount and type of alcohol consumed, the time period over which alcohol was consumed, and
  • personal characteristics such as age, weight, alcohol tolerance, and food intake.

In any case, the court must determine the relevancy of testimony about retrograde extrapolation. The admissibility of retrograde extrapolation evidence often depends on whether enough factors affecting the calculation are known. Calculations that rely solely on average rates of absorption and excretion are problematic, Factors used in evaluating the reliability of retrograde extrapolation include:

  • the length of time between the offense and the test administered;
  • the number of tests given and the length of time between each test; and
  • whether, and if so, to what extent, any individual characteristics of the defendant were known to the expert in providing his extrapolation.

These characteristics and behaviors relevant to retrograde extrapolation might include, but are not limited to the following factors:

  • the time of the last drink;
  • the person's typical drinking pattern and tolerance for alcohol;
  • the person's weight; 
  • the person's gender;
  • how much the person had to drink on the day or night in question;
  • what the person drank; and
  • the duration of the drinking span from start to finish.

While a person's blood alcohol level will rise even after he or she stops drinking, once the absorption phase ends, the blood alcohol levels decline. In most cases, the absorption process generally requires one to three hours. Once a person completes absorption and enters the elimination phase, blood alcohol levels decline in a linear fashion.

Attorney for DUI Cases and Retrograde Extrapolation

If your DUI case involves a breath or blood alcohol concentration result, make sure your attorney is familiar with the theory of retrograde extrapolation and how the science can be used to show a reasonable doubt about whether your BAC was over the legal limit at the time of driving.

Call (702) 385-3131 to speak with James C. Gallo, an experienced DUI attorney in Las Vegas, about the facts of your case and defenses that can be used at trial. In a DUI breath test case or a DUI blood test case, understanding retrograde extrapolation and using it to your advantage can make all the difference in how your case is resolved. Call to discuss your case in Clark County, Nevada, including the City of Las Vegas, the City of North Las Vegas, the City of Henderson or the Clark County Township.


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