Edited sentence: A blood sample of approximately 10 cm³ is usually sufficient to screen and confirm most common toxic substances.A blood sample provides the toxicologist with a profile of the substance that the subject was influenced by at the time of collection; for this reason, it is the sample of choice for measuring blood alcohol content in drunk driving cases.A urine sample is quick and easy for a live subject, and is common among drug testing for employees and athletes.An example of this is THC from cannabinoid (for example, marijuana) use, which in heavy users can be detected in urine for up to 14 days following use.Drugs and pharmaceuticals that are highly protein bound in blood will have a lower concentration in oral fluid.Note also that it can take as long as 8 hours until a given substance can be detected.Oral fluid is composed of many components and concentrations of drugs typically parallel to those found in blood.Oral fluid is the proper term, however saliva is used commonly.Saliva is a component of oral fluid.Sometimes referred to as ultra filtrate of blood, it is thought that drugs pass into oral fluid predominantly through a process known as passive diffusion.Specific to workplace drug testing, urine collection MUST be directly observed due to the prevalence of substance abusers "beating the test" via sample substitution or adulteration.The use of oral fluid is gaining importance in forensic toxicology for showing recent drug use, e.Urine samples do not necessarily reflect the toxic substance(s) the subject was influenced by at the time of the sample collection.in clinical settings or investigation of driving under influence of substances