Drug Testing - The Definitive Guide
SCREENING FOR ILLEGAL SUBSTANCES
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, DHHS Certified labs are accurate. Clinton writes:
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 lab that simply reports 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 as low as 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 do not know which 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.
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 Federally regulated jobs require high laboratory 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. The good news is that even certified labs have perfected the testing process so much that their pricing matches or beats that of non-certified laboratories. A list of certified labs can be found at: http://dwp.samhsa.gov/DrugTesting/Level_1_Pages/CertifiedLabs.aspx
Procedures used
In the workplace, an EMIT or immunoassay screening is typically used, with a CG/MS confirmation if the EMIT or immunoassay is non-negative. However, this is not a rule; employers can, and some do, use unusual procedures. Some employers use hair test and still others use saliva testing.
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 at about 5%. 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 causes of false positives here, but the most common cause are over-the-counter or prescription medications.
