Drug Screen Information
1. Immunoassays
Instant drug screens are competitive immunoassays in which various drugs of abuse compete
for antibody bonding sites with conjugate drugs on the drug screen test strips. Instant screens
are considered “Dry chemistry” because the chemicals necessary to detect the presence of
drugs are dried onto the antibody pads and test strips. If the target drug is present at or above
the drug screen cut-off concentration, the antibody bonding sites will all be taken by the
target drug present in the urine specimen. Therefore, there will be no antibodies left to bond
with the conjugate or dummy drug on the test strip and NO LINE WILL FORM for that
specific drug. If the target drug is not present at a concentration at or above the drug screen
cutoff, then the unbound antibodies (which are bound also to colloidal gold dye) will bind to
the conjugate drug on the test strip in a colorimetric reaction creating a visible line called the
TEST LINE. The presence of any colored line, no matter how faint, indicates a negative
result for the drug beside that line.
The initial drug screen cutoff levels and GC/MS (Gas chromatograph/Mass Spectrometry)
confirmation levels are provided below:
Drug
Screen Cutoff
THC
50 ng/ml
Cocaine
300 ng/ml
Opiates
2000 ng/ml
Amphetamines
1000 ng/ml
Methamphetamines
1000 ng/ml
Benzodiazepines
300 ng/ml
Barbiturates
300 ng/ml
PCP
25 ng/ml
Methadone
300 ng/ml
Tricyclic Antidepressants 1000 ng/ml
GC/MS Confirmation Cutoff
15 ng/ml
150 ng/ml
2000 ng/ml
500 ng/ml
500 ng/ml meth + 200 ng/ml amp
200 ng/ml
200 ng/ml
25 ng/ml
300 ng/ml
1000 ng/ml
THC stands for Tetrahydrocannabinol. Initial screens including laboratory initial screens
and instant screens are sensitive to several metabolites, but the GC/MS confirmation is more
specific and looks for only one specific metabolite. For example, the marijuana screen reacts
primarily to 11nor-delta9-THC and 11nor-delta8-THC and also other THC metabolites. But
the GC/MS confirmation for THC looks only for 11nor-delta9-THC. Other confirmations
require multiple GC/MS analysis’ for multiple metabolites. For instance, an opiates GC/MS
confirmation must be done for morphine, codeine, hydromorphone, hydrocodone, and
oxycodone. Although not all labs conduct the latter three tests as standard procedures.
Similarly, several GC/MS confirmations must be performed for benzodiazepines and
barbiturates. Laboratories differ in which benzodiazepines they confirm for. These differing
confirmatory compounds and the fact that the labs can only confirm for any specific
compound down to 200 ng/ml results in benzodiazepines being the most difficult drug to
confirm for, because most screens react to nordiazepam and some other bezodiazepine
metabolites at a level below 200 ng/ml. The primary or target metabolite of the instant
screens is oxazepam, which reacts at 300 ng/ml.
1. Re-screening vs. GC/MS confirmation
All positive initial screens should be confirmed by GC/MS (Gas Chromatagraph/Mass
Spectrometry) at a DHHS/SAMHSA certified laboratory. This is due to the fact that any
laboratory or on-site/instant drug screen, no matter how accurate, is not 100% accurate in
identifying drugs of abuse in urine. The initial screens react to multiple drug metabolites, and
can under certain non-ideal situations, produce a positive result when the target drug is not
present or is present at a level below the GC/MS confirmation cut-off level. GC/MS
confirmation is a more specific test that looks for and if present quantifies the target metabolite.
It is the GC/MS confirmation through a certified laboratory that will stand up in the court of law
if the drug test result is challenged by the donor.
Some companies who perform instant drug screens attempt to confirm positively screened
specimens by one of two incorrect methods:
1. Sending the specimen to a lab as a “Blind screen” where the specimen will be screened
by the laboratory, and if found positive by the lab screen, will be confirmed by GC/MS at
the lab. The error with this method is that the lab screen may produce a negative result
on a specimen that is near the screen cut-off and that would confirm by GC/MS.
However, the specimen will never be sent to GC/MS for confirmation if the labscreen
calls the specimen “negative”. Therefore, any error or inaccuracy in the lab screen will
result in a “true positive” specimen being ruled “negative”
2. Sending the donor to another collection facility to provide a second specimen that will be
either screened on site or sent to a lab for screening.
a. If the specimen is screened on-site with another instant screen, then the accuracy
of the on-site screen will dictate whether or not the positively screened specimen
is sent to the lab for yet another screen or GC/MS confirmation. If the instant
screen produces a positive result and the collection/testing facility sends the
specimen to the laboratory as a “Blind screen” then a third screen will be
performed on the specimen proving another opportunity for the specimen to be
incorrectly reported as “Negative” due to screen inaccuracies.
b. If the specimen is collected and sent to a lab then erroneous results can be
reported as detailed in “2a” above.
Another fault to be pointed out with sending the donor to another facility for a “Second
collection” and screen is the fact that a subsequent urine catch will probably have a lower
drug concentration than the specimen that initially screen positive on the initial instant
screen, and that an opportunity is provided for the donor to “Hydrate” themselves by
drinking mass quantities of fluids or by drinking a “Flush” drink. Both of these tactics
can significantly reduce the concentration of drugs in the urine and increase the chance
that the drugs will not produce a positive drug screen and/or GC/MS confirmation result.
Also the donor may attempt to get a specimen from another party that they may attempt
to pass of as their urine. And finally, the donor being afforded additional time, may
attempt to adulterate the specimen with bleach or another adulterant that can be
purchased at a health food store or “Head Shop”. These adulterants may or may not be
detected by the collection/test facility or laboratory.
Medical Review Officers
A medical review officer (MRO) is a physician that has been trained and certified to interpret
and report drug screen results. If the lab reports a specimen as negative, the MRO signs off on
the negative drug screen result. The MRO is responsible for calling a donor who has produced a
positive urine specimen after the lab has reported the confirmed positive result. The MRO must
ask the donor if there is any reason they can provide to justify the positive drug screen. In the
case of marijuana or cocaine there is virtually no justification (except the very rare possibility of
marinol, which is a prescription drug containing marijuana that can be prescribed for post
chemotherapy nausea or possibly glaucoma). For positives that can result from prescription
drugs, the MRO must determine if the donor has a prescription for a drug that would cause the
positive drug screen result. If the donor claims to have a prescription for a drug that could have
caused the positive result, then the MRO must obtain a copy of the prescription form the doctor
or the pharmacy that issued the prescription. If the prescription is deemed to have caused the
positive result, then the MRO reports that the drug screen was “Negative”.
If the donor were to claim that they had a methamphetamine positive because they used a Vicks
inhaler, then the MRO would order a d/l isomer separation to determine if the drug present in the
specimen is at least 80% l-methamphetamine. If the specimen contains more than 20% dmethamphetamine, then the donor is to be considered positive for illicit methamphetamine use.
If a donor is positive for opiates and confirmed by GC/MS to contain hydrocodone and the
donor’s doctor or pharmacist produces a prescription for codeine, oxycodone or some opiate
drug other than hydrocodone, then the MRO must report the drug screen as positive for opiates.
An MRO also serves to redirect the donor’s specimen to a second certified laboratory in the
event that the donor challenges the accuracy of the laboratory result. The MRO must then look
at the drug test results form the second laboratory and determine if they are consistent with the
findings from the first laboratory,
DOT drug screens require that an MRO report all drug screen results including all negative
results.