Blood Alcohol Tests: Collecting the Blood
The first step in the blood collection process is decontamination of the area where the blood will be drawn. In clinical use a prepackaged 70% isopropyl alcohol pad is the preferred antiseptic. However, Betadine (povidone-iodine) is the swab of choice for forensic blood draws. If Betadine is used, it must be allowed to dry prior to the puncture. Studies have shown that sloppy swabbing of an injection site will increase a blood alcohol concentration.
Most forensic laboratories purchase 10 milliliter gray top tubes containing 100 mg. sodium floride, a preservative, and 20 mg. potassium oxalate, an anti-coagulant. Therefore, when 10 ml. of blood is drawn, the concentration of preservative is one percent. A tube with an anti-coagulant should be inverted at least eight times (eight to ten is usually recommended). If this is not done, the anti-coagulant will not properly mix, resulting in a low concentration, which in turn can lead to microclotting and an inaccurate result. This is not just the wishful thinking of a defense attorney but is included in the instructions issued by the manufacturer of the blood alcohol collection tubes used in Georgia.Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website