Sorry you are out of your league on this one. Below is a study I was very much part of back in 1998.
TEST STANDARDS AND ACCURACY
The accuracy of drug testing is an area where I've decided to neglect all statistics. Those who oppose drug testing provide numbers indicating a high level of false positives. Those who favor drug testing provide numbers indicating high levels of accuracy. The fact is that accuracy varies widely from lab to lab. Generally speaking, NIDA labs are accurate. NIDA (The National Institute of Drug Abuse) is the government organization responsible for regulating the drug-testing industry. The vast majority of urine drug screens done these days conform to NIDA specs, and ALL testing associated with the government (department of transportation, etc.) complies with the NIDA standard. It is NIDA that decides what the "safe" cutoffs are to avoid false positives.... Despite what you might hear on the net, urinalysis, if done correctly, is a very accurate scientific procedure. I know of no labs that simply report the results of the initial EMIT screening without confirming the sample on GC/MS. The fact is, labs WANT you to test negative, because then they only have to run an EMIT test on your urine (a few cents). If you test positive, they must then confirm the positive result on GC/MS, which is considerably more expensive. . . . Incidentally, the machine which tests the hair is a relative of the GC/MS, but is FAR more precise. It can accurately detect levels of THC in a solution that are below 1 ng/mL!
CAP (College of American Pathologists) also certifies laboratories the way NIDA does. NIDA keeps it's labs in check by sending positive and negative double-blind samples. Lab personnel does not know what samples came from NIDA. If the lab results are wrong, NIDA may take away the labs certification. Only labs that perform the GC/MS on site can be NIDA certified. Labs that send samples to another laboratory for GC/MS confirmation are ineligible for NIDA certification. "Drug testing when done properly with all required controls and confirmation procedures is very accurate and reliable" (anon1).
Not all labs are NIDA/CAP certified. Some labs do not properly and thoroughly clean the GC/MS equipment. Some labs don't even do a GC/MS confirmation! Some labs use cheap alternative methods to reduce expenses.
Many human errors occur in labs and cause inaccurate results. Some are careless or irresponsible errors, and some errors are accidents. Human error can ruin the results of ANY test, screening or confirmation GC/MS.
The only lab you should be concerned with is the one that is testing you. Only Federal jobs require NIDA standards. Your typical private employer may use any lab s/he chooses, which would very likely be the least expensive. Businesses don't always choose NIDA labs that follow-up a positive screening test with a confirmation GC/MS.
Procedures used: In the workplace, an EMIT screening is typically used, with a CG/MS confirmation if the EMIT is positive. However, this is not a rule; employers can, and some do, use unusual procedures. Some employers use the RIA, and some use the hair test. The government uses RIA. They may or may not supervise the subject. Olympic athletes must be monitored by courier after a competition. The courier stays with the athlete until the athlete urinates, with a time frame of up to sixty minutes.
False positives: No laboratory process is completely free from error. The GC/MS test is virtually error free, but the EMIT is far from accurate. There are some false positives you should avoid if you're getting an EMIT test. Take this seriously; false positives run high. If you know that there will be a GC/MS confirmation test, you can disregard this section. It would be too lengthy to list all of the false positives here. Jeff Nightbyrd's "Conquering the Urine Tests" pamphlet lists a majority of the false positives in detail. (If you are clean, want to get back at the testing industry for conducting these absurd tests, and know that there will be a confirmation test, you could consume several false positives. This would force labs to pay for the high priced GC/MS test, eventually drive up test expenses. You will still pass the test as long as you didn't use any true positives.)
Ibuprofen: Ibuprofen is a common pain reliever that (even in low dosages) used to cause a false THC positive on the EMIT test. The EMIT has been changed to use a different enzyme to eliminate false positives due to Ibuprofen. Ibuprofen in very high doses will still interfere with both the EMIT and the GC/MS. There is some conflicting data here because some sources say that the GC/MS tests can distinguish between Ibuprofen and THC (as well as other over-the-counter drugs).
Cold remedies, pain relievers, hay fever remedies, & diet pills: Decongestants and diet pills result in false positives for amphetamine use in one third of the test samples given to 40 of the countries leading laboratories. There are roughly 300 over-the-counter drugs that cause false positives on the EMIT.
Antibiotics: Certain antibiotics (like Amoxicillin) are claimed to cause a positive for heroin or cocaine. My expert source was unable to verify this, so I regret that there is some uncertainty here.
Melanin (black skin): Melanin is the brown pigment that protects your skin from UV rays. It was raised as a discrimination issue in the 1980's, and argued that melanin's molecular structure is similar to that of a THC metabolite. Subsequent research revealed flaws in the data. Melanin was found to have no effect on THC metabolite testing.
DHEA: DHEA taken by AIDS patients will cause a false positive for anabolic steroid use.
Dental treatment: Caine products (like novacaine) used in dentistry have been known to cause false positives for cocaine.
True positives (legitimate): Some legal products actually contain small amounts of illegal chemicals. All tests, including the GC/MS, will test you positive because the metabolites derived from the true positive are identical to the metabolites of the illegal drugs. One exception: poppy seeds will not cause a positive GC/MS (explained below).
Poppy seeds: Poppy seeds, usually on breads, contain traces of morphine, and lead to positives for opiates. According to Dr. Grow, eating a pastry filled with poppy seeds will bring results showing that you are a *high level* opiate user. Harold Crossley, a nationally known chemical dependency expert, said you would have to eat 100 poppy seed bagels to score a positive on a drug test. When taken into account that very few poppy seeds are sprinkled on bagels, you can see that poppy seeds from a hundred poppy seed bagels will easily fill a single large pastry. Purim cookies, a Jewish food known as Hamantashen, may have five to six tablespoons of poppy seeds. A couple Purim cookies may cause a positive test. Poppy seeds can be distinguished from illicit drugs on the GC/MS test. Although poppy seeds have the same metabolites as opium, these metabolites are shown to have different patterns when viewed with the GC/MS.
Testosterone supplements: Orchic extract (found in bull's balls) will give a positive for anabolic steroid use. It is a legitimate substance that causes the test to imply that you abuse steroids.