Grading the Tests
Urine
Collection
Urine specimens are collected in a restroom. Same-gender testing monitors are present to inhibit adulteration, substitution or dilution of specimens. Direct observation of the sample collection is rare, but can be used when there is reason to suspect tampering may occur.
Efficacy
Urinalysis is the most widely used and least expensive drug testing method, with each test costing as little as $10. It is the preferred method for federal employers and contractors. Urine tests can detect most drugs for three to seven days. Analysis can target almost any drug, from opiates to nicotine.
Collection
A small amount of hair is cut from the back of the subject's head by the collector. Collection does not require special training. Samples do not require refrigeration, and face no biohazard restrictions. Hair testing is perhaps the least intrusive method, and makes adulteration or substitution by the donor impossible.
Efficacy
Hair testing is much less common than urine testing, and costs substantially more. Although hair analysis can find evidence of past drug use up to ninety days, very recent use may not be detected. Some research has shown that passive exposure to drugs (e.g., second-hand marijuana smoke) may produce false positives.
Saliva
Saliva is collected on an oral swab, under direct observation of a testing monitor. Swabs can be bagged and shipped for analysis, or evaluated by an on-site device. Test is minimally intrusive, leading some schools to choose saliva over urine. Adulterating or substituting samples is impossible.
Efficacy
Drug residues and metabolites do not remain in saliva as long as in urine, so the test only detects very recent use, up to twenty-four hours. Cost is comparable to urine testing. Some studies have shown saliva tests are relatively insensitive to marijuana, leading to a high percentage of false negative results.
Sweat
Collection
An adhesive patch like a band-aid, worn for up to two weeks, collects sweat for later analysis. A semi-permeable membrane allows skin to breathe, and the patch is designed so that it cannot be removed and reattached. Sweat testing is most often used to monitor former users in treatment facilities or on conditional release. Tampering is very difficult. Specimen-gathering is non-invasive.
Efficacy
Patch can detect low levels of drug residues for as long as it is worn. Some subjects may experience a harsh reaction to the patch. Passive exposure or residues on the skin surface may produce false positives. There is no widely accepted legal standard for sweat patch tests, and U.S. courts have varied on accepting them as evidence.