How does drug testing work?
Urinalysis uses a drug screen and then (usually) a drug test to detect metabolised drugs in the urine sample. Basically, a drug enters the body in its psychoactive form, and come out as a metabolite. It is these metabolites which are found in the urine, as the drug itself has been broken down.
Take for example cannabis: the ingredient that gets you high is the THC, 11-nor-D-9-tetrahyrocanibinol, which travels from the lungs into the blood stream, and then is absorbed into fat cells. It is then stored in these cells until they are burned for energy, when they are released back into the blood stream (This is why marijuana can be detected for some time after consumption). This metabolised marijuana is divided into about 30 different metabolites, the most common of these being THCA, 11-nor-D-9-tetrahyrocanibinolic acid. These metabolites are then detected in the urine using a screen test (spectrometry), and then if the levels are high, either gas chromatography or mass spectrometry.
The number of metabolites produced by different drugs varies, from 1 for phencyclidine, to 4 for cocaine, 5 for amphetamines and 31 for dope.
Whilst the drug derivatives are in the bloodstream, they become trapped inside the growing hair follicles as the blood feeds growing hair. Drug tests from hair are taken from the nape of the neck as this is where the drug is most concentrated. The hair is dissolved by organic solvents which frees up the trapped metabolites. The results of the testing on hair is usually used in correllation with urine testing to produce a more accurate result.