Breathalyzer versus Blood Tests in Drunk Driving Cases
The most frequently used test in drunk driving cases is the breath test or Breathalyzer test. The breath test is used more frequently than urine or blood tests to test for the blood alcohol level because it is less intrusive and the apparatus is easily portable and convenient to use, even in the field. Because blood tests are universally relied upon as stronger evidence than breath tests, the prosecution will seek it whenever it can. In many states, a blood test may only be administered in cases involving death or serious bodily injury, or when the motorist required medical treatment and the administration of a breath or urine test was impractical or impossible. Although a motorist may refuse this test, the refusal is usually admissible in evidence against the motorist at the administrative or judicial hearing.
Whether the prosecution seeks to admit the results of the breath test or the blood test, the prosecution must establish that the test sample was the same sample as the one withdrawn from the motorist, (the chain of identity), and that the authorities complied with all of the statutory prerequisites to admissibility that are set forth in the chemical test legislation enacted in the jurisdiction.
With respect to breath tests, in order to admit the results of a breath test into evidence, the prosecution must prove several things: (1) the operator was qualified to use the apparatus; (2) the breathalyzer equipment was correctly maintained and in proper working order at the time of the test; (3) the breathalyzer was, in fact, an approved model; (4) the ampoules contained properly compounded chemicals and were spot-checked, tested, and certified; and, (5) the test was conducted according to methods and procedures approved or specified by regulations or department of health standards. A number of factors may affect the accuracy of the results of a breath alcohol test. These include regurgitation, belching, and the passage of time since last consuming alcohol. Most states have incorporated a "20-minute" rule to prevent such things from interfering with an otherwise valid breath test results. This rule requires the testing officer to observe the motorist for 20 minutes prior to testing in order to ensure that he or she does not ingest anything that would undermine the test results.
In almost all instances, the most accurate determination of the concentration of alcohol in blood is obtained by analysis of the blood. Blood-alcohol analysis in forensic laboratories typically employs gas chromatography which can be highly specific for alcohol and quite accurate. Typically, however, blood analysis is done by a central laboratory, and not at the police station. Breath testing, in contrast, can readily be carried out at the police station and generally does not require collection and transportation of specimens to another location, which raises chain of evidence issues. With respect to blood tests, it is the prosecution's burden when introducing the test results to establish the following predicates: first, that the test was reliable; second, that the test was performed by a qualified operator with the proper equipment; and third, that expert testimony was presented concerning the meaning of the test.
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