In Pennsylvania, blood testing for alcohol concentration is preferred in a number of counties over breath and urine testing. Typically, a police officer will take a person following an arrest to a hospital to have blood samples taken. Other times, the police departments have officers who have been trained to extract blood samples in a medically safe manner. At a hospital, a nurse or blood sample technician (phlebotomist) will extract two blood samples. These blood samples are either tested at the hospital or transferred to the arresting police officer.
That officer should transport the blood samples immediately to the police department for refrigerated storage. Subsequently, the samples are taken to a forensic laboratory for blood testing. Once at the laboratory, the blood samples must be stored in a refrigerated evidence vault.
At the laboratory, a forensic chemist will typically test the blood samples for alcohol concentration using headspace gas chromatography. Due to the quantity of driving under the influence arrests, the laboratories will often take weeks to conduct the blood testing for alcohol concentration. Many police officers will wait for the blood testing alcohol concentration results before filing a criminal complaint charging DUI.