Before a blood test result may be admitted by your trial judge into evidence against you, the prosecutor must be able to cross several "hurdles" that your defense lawyer may raise. At each point in the prosecutor's offer of proof that the blood test was properly collected, stored, refrigerated and tracked (as it goes in and out of the laboratory's refrigeration units), your defense attorney will be challenging the completeness of the State's record-keeping and the scientific propriety of each step.
The proper taking of blood
For blood alcohol tests (as opposed to blood tests for drugs), it is essential that the blood be drawn in a correct manner, using a brownish-red colored solution (Betadine) or white (Hibaclens) soap rather than an alcohol pad or swab. If alcohol is used to prepare your skin before the needle insertion, then this may artificially raise the alcohol content in the sample due to contamination by the alcohol on the surface of your skin. The additive effect from such an alcohol-based swab has been reported to be as high as 0.16%.
Next, the receptacle in which a "legal" blood alcohol must be collected and held is a grey-top tube. These tubes are most often "Vacutainers(R)," a product manufactured by Becton-Dickinson. The color of the top (the rubber stopper) is very important in this blood collection process.
Blood must be tested quickly
Red-stopper tubes are also used by hospitals (for many of their testing procedures) for a determination of your blood alcohol level, and also for some drug screens. However, because these tubes have no chemicals added as preservatives or anti-coagulants, any tests must be run on the blood samples in these tubes within a few hours due to the fact that the blood will clot and otherwise become putrid and decompose very quickly. As mentioned in the previous section, when blood putrefies, it decomposes into a variety of by-products. One of these by-products generated is the production of ethanol (alcohol). This alcohol is indistinguishable from any alcohol (ethanol) that you drink.
Red tubes must be used
One of the differences in a grey-top tube is that these vials contain one of several powdered or liquid preservatives. Scientists call these chemicals, as a category, "bacteriastats." A properly mixed vial of your blood and these bacteriastats will be "stable" for several days or even weeks, especially if properly refrigerated.
Procedures for testing blood
Whoever draws (collects) your blood must gently invert the tube to mix this preservative with your blood immediately after drawing it. This is typically done by gently inverting and rocking the grey-topped tube 12 to 15 times to assure dissemination of the powder or liquid throughout your blood. Incomplete mixing of all of the powdered or liquid preservative can lead to putrefaction and decomposition. Shaking the tube too vigorously can cause the structural components of the blood cells to break down. Such "breaking open" of the cell structures can lead to flawed results when the sample is analyzed.
Wrong tube as a defense
Another defense your attorney may raise deals with using the incorrect type (colored stopper) of tube. Most state crime labs mandate the color of the stopper in the test tube so that decomposition of samples that sit in the lab for a long time is minimized due to being mixed with powdered or liquid chemicals designed to retard bacterial growth. Your DUI-DWI defense attorney will know what your state's regulations or rules mandate for the blood collection vial's stopper color.
Wrongly performed blood procedures as a defense
If the blood was not inverted correctly so as to mix with the preservative and anti-coagulant, then any results can be challenged by your defense attorney. The attorney will use cross-examination of the prosecutor's witnesses to start creating "reasonable doubt." Then, expert witnesses may be called to testify on your behalf to show how the flawed handling of the blood likely could result in a falsely elevated blood alcohol reading. If the tests are not scientifically credible, then the alleged alcohol reading should not be used against you at trial. [See more ideas from the checklist contained in Appendix I.]
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