Urinalysis Drug Tests

Testing is most frequently performed on small samples of urine,
although hair, saliva, and blood can also be used. Urine samples are
collected by personnel under carefully controlled circumstances to
avoid mismatches resulting in false positives, and to prevent
adulteration of the specimen by the swapping of samples or the
addition of foreign substances. In particular, urine samples heavily
diluted with water can skewer results, and so highly diluted specimens
are routinely rejected. In certain legal cases involving individuals
known to be repeat drug offenders, personnel are usually required to
witness the sample being provided in order to ensure that no
adulteration has taken place.

Samples can be tested at the same site in which they were provided.
More frequently, it is shipped to a large facility that specializes in
mass-testing specimens. Care must be taken in shipping to ensure the
integrity of the specimen, and those that indicate contamination are
not processed. A special tamper-proof seal is routinely placed on
bottles to indicate whether or not this has occurred
http://www.getgift.com.cn/Drug-Testing.htm