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 shown below:
|Drugs and their cut-off level.|
|Drug||Screen Cutoff||GC/MS Confirmation Cutoff|
|Marijuana (THC)||50 ng/ml||15 ng/ml|
|Cocaine (COC)||300 ng/ml||150 ng/ml|
|Opiates (OPI)||2000 ng/ml||2000 ng/ml|
|Morphine (MOR)||300 ng/ml||2000 ng/ml|
|Amphetamines (AMP)||1000 ng/ml||500 ng/ml|
|Methamphetamine (MET)||1000 ng/ml||500 ng/ml|
|Benzodiazepines (BZO)||300 ng/ml||200 ng/ml|
|Barbiturates (BAR)||300 ng/ml||200 ng/ml|
|Phencyclidine (PCP)||25 ng/ml||25 ng/ml|
|Methadone (MET)||300 ng/ml||300 ng/ml|
|Tricyclic Antidepressants (TCA)||1000 ng/m||1000 ng/ml|
|Ecstasy (MDMA)||500 ng/m||500 ng/ml|
|Oxycodone (OXY)||100 ng/m||100 ng/ml|
|Propoxyphene (PPX)||300 ng/m||300 ng/ml|
|Buprenorphine (BUP)||10 ng/m||10 ng/ml|
|Spice (SCA)||50 ng/m||50 ng/ml|
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.
Drug screen 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 lab screen 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% d-methamphetamine, 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.