Blood toxicology is usually used to determine the presence of drugs within a person's blood stream. It may also be used to check for the presence of others substances.
There are a variety of blood screens that can measure the levels of various foreign substances (things that ought not be there) in the bloodstream. A physician (or coroner) can request any number of blood toxicology tests to check for drugs/alcohol, poisons/chemicals and other substances that may be suspected in causing a variety of problems, including impairment and/or death.
Alcohol, amphetamines, barbiturates, benzodiazepines, cocaine, codeine, heroin, hydromorphone, methadone, morphine, phencyclidine, propoxyphene, tetrahydrocannabinol, are measured in a blood toxicology test