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Retrograde Extrapolation 

A recent version of the Toxicology Standard Operating Procedures were issued by FDLE's Forensic Quality Manager on January 13, 2015, in version TOXSOP15. Unit 3 of the TOXSOP15 deals with technical calculations review and retrograde extrapolation.

The procedures contained in the Toxicology Standard Operating Procedures applies to retrograde extrapolation calculations performed in the laboratory. The requirements include:

A. Prior to performing any retrograde extrapolation calculations, the analyst shall collect all required information. The following is the minimum required information to perform a retrograde extrapolation calculation: 

1. An FDLE determined blood alcohol concentration result from a specimen submitted to the FDLE laboratory. Retrograde extrapolation calculations will not be performed on alcohol levels of 0.030 g/100mL or less. 

2. The time elapsed between the incident and the blood specimen collection. 

3. An estimate of the time of the last drink. 

B. If all of the required information above is not provided, a note will be placed in the narrative of the LIMS that the service was requested but could not be performed. 

C. If a calculation is to be completed, the analyst should attempt to obtain the following information that may have an impact on calculations and/or interpretations: 

1. The drinking history prior to the incident;

2. The type and number of beverages that were being consumed by the subject;

3. The time and content of the subject’s last meal prior to the incident; and

4. The age, height, weight and sex of the subject.

D. The FDLE Retrograde Extrapolation Request Form shall be utilized to document all information collected and shall be retained in the case file. 

E. A report shall be issued showing the result of the retrograde extrapolation calculation rounded to two (2) decimal places using conventional rounding. If the required information listed in ‘A’ is provided but deemed inappropriate for performing a retrograde extrapolation calculation, a report shall be issued stating that the retrograde extrapolation could not be performed along with the reason why.

 F. Prior to the release of retrograde extrapolation results, the calculations and information used to perform calculations shall go through technical and administrative review. The reviews will cover at least the following: 

1. The information used to perform the calculations;

2. The appropriateness of performing the calculation;

3. The appropriateness of elimination rate(s), volume of distribution(s), and other factors used in calculations;

4. The arithmetic; and

5. The scientific basis of the opinion(s).

G. The case record shall include: 

1. Who the analyst obtained information from and the date(s) it was obtained;

2. All information listed above that the analyst was able to obtain;

3. Elimination rate(s), volume of distribution(s), or other factors the analyst used in calculations;

4. Detailed calculations and date(s) that the calculations were performed;

5. A clear indication of the analyst’s opinion(s); and

6. A record of the administrative and technical review, including who conducted the review and the date that the review was done.

Select References: 

1. Medicolegal Aspects of Alcohol, James C. Garriott, editor. Lawyers & Judges Publishing Company, Inc. 

2. Principles and Application of Medicolegal Alcohol Determination, Widmark. Biomedical Publications. 

3. “Pharmacokinetics of Ethanol – Issues of Forensic Importance,” A.W. Jones, Forensic Science Review, V.23 (2), 2011. 

4. “Calculation of Blood Alcohol Concentration (BAC) by Sex, Weight, Number of Drinks, and Time,” Fisher et al., Canadian Journal of Public Health, 78, 1987.

A more complete list of requirements can be found in the Toxicology Training Manual.


Attorney for Retrograde Extrapolation in Florida DUI Cases

If the prosecutor in your case is attempting to admit evidence of retrograde extrapolation in your DUI case in Tampa, FL, then contact an experienced DUI defense attorney at Sammis Law Firm. 

Our attorneys fight DUI cases in Tampa, FL. We represent clients charged with DUI after a blood test, including both the medical blood test to determine the BAC or a legal blood test after the sample was drawn at the request of a law enforcement officer. 

Contact us to discuss the best ways to fight these types of complex DUI cases. 

Call 813-250-0500.


This article was last updated on Friday, August 31, 2018.