Like previous tests these levels are different for every person and every lifestyle. Water intake, exercise, metabolism, and consistency of use all effect the level of nanograms reported for a person. Of these, metabolism plays perhaps the most crucial role; since THC is a fat soluble chemical (meaning it stores in fat) it can actually be “burned” off quicker or slower depending on the body’s metabolism level. For example an athlete would on average have a lower level than someone of less physical activity with the same amount of use.

Does this really change anything? Amazingly yes, now instead of person simply being labeled an “addict” the drug test will reflect a more accurate portrayal of that person and their substance abuse. Now a potential employer can tell whether a person uses everyday, not at all, or just every once in a while. Many have suggested that the use of this drug testing might actually be positive for most people who use looking for employment. Statistics have shown that employers’ at most low skill jobs (like cleaning, delivery, and other tedious work) don’t really care if a person uses recreational drugs like Marijuana as long it happens infrequently. This test may prove to be revolutionary, for in the past it was not possible to really differentiate between a casual user that will be productive and a true substance abuser.

Reasonable suspicion testing is used by employers who have a legitimate reason to think an employee is using drugs. Observable symptoms of drug use, erratic behavior, or excessive absenteeism can all provide a basis for reasonable suspicion testing. Post-accident drug testing is used in the immediate aftermath of an on the job accident. This type of employment drug testing is crucial because, more often than not, on the job accidents result in property damage or personal injury. In these cases, liability becomes the main issue and determining if any of the parties involved were influenced by drugs or alcohol can protect employers from unscrupulous lawsuits or worker’s compensation claims. Return to duty drug testing is used when an employee is returning to work from a long period away, perhaps for maternity leave or a personal sabbatical. This type of employment drug testing should also be used for employees who have failed a drug test previously and have completed the necessary counseling and recovery efforts.

http://www.dol.gov/asp/programs/drugs/workingpartners/dfworkplace/dt.asp