DUI arrestees often choose blood testing. The blood draw either occurs at a jail infirmary or at a hospital. Some sort of non alcohol solution must be used to swab the injection site--this is usually not an issue--they know how it's supposed to be done.
Most DUI arrestees are released from the jail either on their promise to appear or by posting bail. Court dates (for arraignment) are usually set about a month away although that can vary depending on the court and law enforcement agency involved.
Who analyzes the blood for alcohol content? LAPD's SID does the analysis for those arrested within the City of Los Angeles and the Sheriff's Crime Lab in Downey analyzes for most other police agencies. Long Beach has their own crime lab.
What happens if the blood analysis is not performed in time for court? In most cases the analysis is performed in time for the prosecutor's office to do their filing review. But where the lab is backed up and the turn-around time from arrest to arraignment is on the short side, no result will be available. In such cases, the prosecutor will generally NOT file a case in court by the due date. When that happens no one need appear (except in Ventura County where they do require an appearance) since the judge will have no case to call. When the blood result is finally delivered to the prosecutor, that office will file the case in court (if the result is high enough) and send a letter to the arrestee with a new court date about 30 days from the date the letter is mailed.
What happens if the arrestee has moved? If that happens and no forwarding address has been established, then the court will likely issue an arrest warrant for the defendant when there is no appearance on the date the DA specified in the letter. It's best to periodically check (or have your lawyer check) witht the DAs office to determine the status. You certainly do NOT want to be arrested again--the first time was enough.