A Comparison of Blood Alcohol Levels as Determined by Breath and Blood Tests Taken in Actual Field Operations

Report No: 72-R4

Published in 1972

About the report:

During its 1972 session, the General Assembly of Virginia enacted Senate Bill 104, which authorizes the breath test, as well as the blood test used previously, as a proper chemical test to determine the alcoholic content of the blood. Any person arrested in Virginia after January 1, 1973 for suspicion of driving while intoxicated may elect to have either the breath or blood sample taken, but not both. In anticipation of the use of the breath test for determining the level of intoxication, the Highway Safety Division of Virginia decided to conduct preliminary field testing of breath-testing devices in conjunction with the Fairfax Alcohol Safety Action Project (ASAP). Increased police surveillance and enforcement against drunken drivers started in February 1972 in the ASAP area. Drunken drivers who were arrested in Fairfax routinely submitted to the blood test for blood alcohol determination, but in addition, each subject was also encouraged to take the breath test, which was not evidentiary at that time. The results of the blood tests from both the Commonwealth's sample and the sample sent by the defendant to a private laboratory were recorded alongside the corresponding reading from the breath test. All of the breath tests were taken on an Intoximeter Mark II, which uses gas chromatography to determine the alcohol content of the breath. The Intoximeter Mark II was equipped with an automatic digital readout from which the results could be read one minute after the breath sample was taken. Two Intoximeters, which were mounted in a mobile van with the blood-drawing equipment, were used for the breath tests. Whenever an arrest was made, a police officer would call the mobile van operator and arrange to meet him, either at the scene of the arrest, at the office of a Justice of the Peace, or at some other prearranged site. A requirement on all the tests was that an arrested subject must wait a minimum of 15 minutes after the arrest before the breath test could be conducted. For the purpose of this analysis, a total of 104 sets of data were used. Each set consisted of the blood alcohol readings from the breath test, the Commonwealth's blood sample, and the private laboratory sample. The results of the breath test were compared to the results from the Commonwealth's blood sample and to the private laboratory blood sample. The private laboratory sample was also compared with the Commonwealth's blood sample. From the comparisons, some conclusions were drawn and recommendations made, as will be discussed in detail in the technical report.

Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.


Other Authors

Thomas J. Smith

Last updated: February 8, 2024

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