Blood Tests

Published: 07th June 2006
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Blood Tests

When a person is arrested for a DUI, that person must submit to a chemical test under the "Implied Consent" provision in the California Vehicle Code. Implied Consent, under Section 23612 states that if a person is lawfully arrested for a DUI, they are deemed to have given his or her consent to taking either a blood or breath to determine blood alcohol content (BAC). If drugs are suspected, a blood or urine test may be demanded.

If a person fails to submit or fails to complete the required chemical testing a number of serious repercussions follow, including fines, mandatory imprisonment if the person is convicted of DUI, and suspension or revocation of the person's privilege to operate a motor vehicle. Even if a person refuses to take a chemical test, courts have given leeway to arresting agencies to take the defendant's blood by a "forced blood draw." Therefore, submitting to the chemical test is in the best interests of someone arrested for DUI.

Even where a person takes a breath test, the officer must advise the person of the right to take a blood test in order to retain a sample of blood for later testing by an independent forensic toxicologist. This is a safeguard for the DUI defendant. Tests are fallible, because they are conducted by human beings. Error is not uncommon. If there are improper levels of preservative in the sample, the blood sample can actually ferment, creating alcohol! If the sample does not contain enough anti-coagulant, the blood will clot. Clotted blood is undesirable for testing because it reflects an artificially high blood alcohol level. Independent testing will reveal such instances. Thus, it is to the DUI defendant's best advantage to have his or her blood sample independently tested.

In order to use blood evidence in a DUI case, the proper procedures must be followed, both before the blood is taken and after. The blood must be drawn by a person certified to take blood. The person's arm must be wiped by an alcohol-free wipe. The kit used to draw the blood must contain a vial with both anti-coagulant and preservative, usually in powder form. Once drawn, the blood sample must be shaken in order to equally distribute the anti-coagulant and preservative. The sample must be kept in a controlled environment in order to preserve the quality of the sample. However, there are no guidelines for the proper storage and transportation of the sample. Therefore, it is beneficial in pursuing a DUI defense to identify the "chain of custody" in order to fully understand who had the sample and when.

The procedure most commonly used to test blood samples is called headspace gas chromatography. This testing is based on the scientific principle of Henry's Law which states that at equilibrium the amount of gas dissolved in a given volume of liquid is directly proportional to the partial pressure of that gas in the gas phase. According to Henry's Law, at equilibrium, in a sealed vessel, volatile compounds in the liquid state will be present in the vapor state at a concentration proportional to the concentration in liquid. By sampling this vapor, i.e., the headspace, through a gas chromatograph, the volatile compound may be qualitatively identified and quantitatively measured. A single headspace injection is split into two capillary columns, each exiting to a flame ionization detector. One column is used for quantity, the other for qualitative confirmation. This method has been determined to be the most accurate.


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