If you have voluntarily or been ordered to give blood as part of a DUI arrest and/or investigation, it is always important to challenge the credentials of the individual who drew your blood. In most states there are statutes requiring that the individual who draws the blood of a defendant be either a doctor, registered nurse or phlebotomist.
For example, it may be that a hospital or clinic was exceptionally busy and an intern drew your blood. This could allow for that evidence to not be included as its integrity can be called into question. Please make sure, that if you do have blood drawn that you note who it was that did the procedure, it could be very valuable in your defense.