Retrograde Extrapolation for the DUI Lawyer

by baronedefensefirm on September 29, 2011

Here is an email question recently received from a new lawyer:

I hope all is going well.  I had a question regarding retrograde extrapolation.  I was told that the statute says we cannot use retrograde extrapolation.  So if a person blows a pbt of .06 at 12:30, and refuses the data master at the station (forgetting about all the implied consent stuff), and cops get a warrant and take person to clinic, and at 1:45 the blood reveals a .10, I was told that retrograde extrapolation is no longer valid because of statutory law, and that the person is presumed to be .10 at the time of the incident.  Is this correct?  I have been trying to look this up.

Here is our answer:

What crazy person told you that??  It’s preposterous really.  The instruction was changed so it says there’s an inference BAC at time of test is same as at time of driving, but what this person is suggesting is that this change creates a presumption, which is not permissible.  (Almost) the only presumption in a criminal case is the presumption of innocence.

Lawyers handling a lot of DUI cases might consider purchasing the BAC-Tracker software.  This software assists in alcohol calculations, including retrograde extrapolation.  The software is provided by BAC-Tracker International, Inc.  Their web site indicates:

We are a forensic consulting company providing forensic alcohol litigation services internationally to the criminal justice community. Headquartered in Atlanta, Georgia, BAC-Tracker International, Inc. provides training, expert witness consultation, and software solutions for the extrapolation of blood alcohol concentration (BAC) and the management of scientific uncertainty for alcohol related cases.

BAC-Tracker International, Inc. has just completed their update to BAC Tracker software v3.1. A.  This update offers a number of additional improvements. The most significant improvements include (1) the addition of a new report type – The Retrograde Alcohol Extrapolation Report. This report will extrapolate the alcohol level to a time of interest from a known BAC; (2) greater freedom of generating reports using various combinations of volume distribution formulae while accounting for uncertainties associated with absorption and/or elimination; (3) and the ability to include the uncertainty associated with the known BAC based on QA/QC data of the analytical method thus allowing BAC Tracker to account for every major source of uncertainty in the extrapolated result.

BAC Tracker v3.1 offers users the ability to generate up to 506 different reports using various combinations of volume distribution formulae while accounting for absorption rates and/or elimination rate uncertainties.

The software can be purchased from the manufacturer’s web site.


This post was written by...

– who has written 204 posts on Michigan Drunk Driving Lawyers.

Patrick T. Barone is the author on two books on DUI defense including the well respected two volume treatise Defending Drinking Drivers (James Publishing), and The DUI Book – A Citizen’s Guide to Understanding DUI Litigation in America. He is also the author of a monthly DUI defense column for the Criminal Defense Newsletter, published by Michigan’s State Appellate Defender’s Office. Mr. Barone is an adjunct professor at the Thomas M. Cooley Law School where he teaches Drunk Driving Law and Practice. He is also on the faculty of the Criminal Defense Attorney’s of Michigan’s Trial Lawyer’s College where he provides trial skills training to Michigan’s criminal defense practitioners. Mr. Barone lectures nationally on various DUI defense topics, and he has appeared in newspapers, on television and on radio as a drunk driving defense expert. Mr. Barone has been certified as an instructor and practitioner of the Standardized Field Sobriety Tests and has also attended a 24-hour certification course at National Patent Analytical Corporation (the manufacturer of the DataMaster) and has thereby been deemed competent by the manufacturer to operate, perform essential diagnostic verifications and calibration checks on the DataMaster. Mr. Barone is a Sustaining Member of College for DUI Defense. Mr. Barone is the principal and founding member of The Barone Defense Firm, whose practice is limited exclusively to defending drinking drivers. The Firm is headquartered in Birmingham, Michigan.

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