Retrograde Extrapolation in Los Angeles DUI Cases

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Trauma resulting from a DUI-related automobile accident has been clearly shown to have a significant impact on alcohol elimination - and thus on the accuracy of any retrograde extrapolation. Consequently, emergency ward physicians must often wait for serum ethanol levels to go down before an accurate neurological or psychiatric evaluation can be performed.

To verify this phenomenon, researchers studied 103 patients who had been admitted to a hospital's emergency unit in an intoxicated condition. They found that the mean rate of elimination of alcohol from the system was 20.43 mg/dl/hr; a standard deviation of 6.86 mg/dl/hr was expected, giving an anticipated range of 13.57 to 27.29 mg/dl/hr. The scientists, however, found a higher rate of deviation: Only 68 percent of the patients fell within the expected range of deviation. Their conclusion: For an accurate prediction of the rate of alcohol elimination in any given individual, it would be necessary to draw a second sample after several hours had passed.

An interesting article entitled Effects of Ethanol: 1. Acute Metabolic Tolerance and Ethnic Differences, 8 Alcoholism: Chemical and Experimental Research 226 (1984), written by Wilson, et al,, describes studies in which elimination rates for alcohol varied depending on a number of factors. Individuals with Oriental ancestry, for example, eliminated alcohol considerably faster than Caucasians. Another variable is reflected in the fact that the elimination rate increased significantly after a second drink - a fact that should add to the increasing evidence that retrograde extrapolation is unrealistic.

An excellent review of extrapolation problems inherent in blood-alcohol analysis in DUI investigations and of the unreliability of delayed testing can be found in Edward Fitzgerald and Dr. David Hume's article, The Single Chemical Test for Intoxication: A Challenge to Admissibility, The Champion 8 (June 1984). The authors discuss the difficulties in extrapolating the blood-alcohol level at the time of driving from the time of testing. Among other conclusions:

The single chemical test for intoxication ought to be excluded as a proof of a defendant's "time of offense" BAG in any case where there is a delay between offense and obtaining a test sample which continues for more than thirty minutes .... As a general rule, a later single test cannot be supported as a reliable indicator of the earlier BAG ....

A second chemical test for intoxication or even a series of such tests will not solve the essential problem, as long as there still remains a significant delay between the time of offense and the first sample collected. However, a second test, perhaps one-half hour after the first, ought to be required by statute when chemical tests are to be used in criminal cases. [pp. 17-18.]

Dr. Dubowski has also summarized the problem with using retrograde extrapolation in DUI cases:

It is unusual for enough reliable information to be available in a given case to permit a meaningful and fair value to be obtained by retrograde extrapolation. If attempted, it must he based on assumptions of uncertain validity, or the answer must he given in terms of a range of possible values so wide that it is rarely of any use. If retrograde extrapolation of a blood concentration is based on a breath analysis the difficulty is compounded. [21 (1) Journal of Forensic Sciences 9 (January 1976).]

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