false positives on u a

i suppose that anything is possible but this doesn't sound correct. the link that incognito gave you is a pretty good one for discovering that type of info.

the hospital where i work has a major university literally across the street. the medical school at this university does all the drug testing for our hospital and is very well renowned for their work in the urine field. i see hundreds of drug tests results every week and have never seen this come up. people are always questioning positive results; i.e. someone who popped +ive for cocaine the other day disputed it saying "that there was people around him smoking crack" which he believed accounted for his results which the university only laughed at.

this is one of those subjects that always has a ton of myths and rumors flying about but i am yet to see one of these be true. 

that is an interesting story.

of course w/in reason there can be false positives like poppy seeds for thc but this is more the exception than the rule.

many times there will be traces of certain drugs as mentioned above but any realiable drug test or tester can determine if that drug was a result of illegal use or simply a bi-product of another source.

it would have been very irresponsible for that doctor to accuse you w/out sufficient proof not to mention extremely unprofessional. however it isn't to say these types of things don't happen.

on a brighter note, most employers use professional/reliable drug testing companys to do their dirty work b/c the nature of its severity.

on a somewhat odd side note, that doctor must have been under the suspicion's that you were on drugs b/c drug these tests are completely different then other types of tests performed on urine. in other words doctors don't order microscopic clean catch test and then they just happen to discover that you had been smoking pot.

on an even odder side note, the majority of drug tests, even the most extensive ones usually only test for cocaine, benzos, opioid, THC, amphetamines.  things like MDNA and PCP are usually specified to look for b/c of suspected use. it is such a bizarre story that it almost sounds like the doctor was setting you up b/c he/she knew that that substance would cause a false positive.

Hi Rob,

Part of my job as a Laboratory Director the last 23 years has been collecting and preforming drug screens both medical and legal.  This is one area that is changing daily almost, which is good and bad for the patient.

FIRST, the chemical naproxen will NOT cause a false positive THC.  Structurally, the molecule is so dissimilar that their will be no reactivity or cross-reactivity such as may occasionally happen.  For instance, occasionally people taking phenylpropanolamine (in cold preps) MIGHT see a false positive with amphetamine because of some structural similarity between the molecules.  Another example is cough syrup with guafenisen and dextromethoraphan cross reacting with the PCP portion of the test.

That being said, the improvements in technology keep things like that from happening more and more.  There are threshold amounts (minimum amounts that react) determined and adjusted in these screening tests which help prevent positive reactions to therapeutic amounts of drugs.  These screening tests aren't meant to pick up every Tom, %^^?, and Harry that take a prescription drug.  For instance, when drug screens first came out, the morphine tolerance was set so essentially, if you took a prescription's worth of Tylenol 3's as prescribed after your root canal, you would have a positive drug screen for morphine.  NOW, that threshold has been raised and raised and raised so that essentially it now picks up only amounts in abusive quantities.  This is to screen out the unconscious person in the ER as a potential overdose or heroin addict vs someone in cardiac failure with a Vicodin prescription taken as directed.

Now, mind you, the above relates mostly to those tests on the drug screen that involve common prescription drugs, i.e. benzos, morphine.  There are lower limits set for barbs and amphetamines as these drugs just aren't that commonly prescribed any more.  Then, there are 0 tolerance limits set on the street type drugs like meth, thc, PCP, methadone.

Also, better technology has made the tests much more specific for the precise chemical or metabolite or both.  The technology and thought behind a drug "screen", though is precisely that, it is too pick up or screen for as many different drugs in each class as possible.  For instance, in a screen, a positive benzo may be the result of 1 of 25 prescribed benzos and there is no way to distinguish which one it is.  For that reason also, trying to make it pick up as many possible chemicals as possible also increases the possibility of cross reactivity.

The saving grace of the drug screen is that if one is positive, it MUST be sent out for confirmatory testing which is done by GCMS or other very precise methodologies.  For that reason, if you are taking cold medicine and your pre-employment screen is positive for amphetamines, it will be sent out for confirmation.  The confirmation will be negative because phenylprop is NOT an amphetamine.  The confirmations are looking for the exact molecule. The laws are very strict on confirmations and testing, especially for pre-emp and legal drug testing.  Chain of custody is another part of the process that is VERY strict.  Your laboratory should not only have policies and procedures for the testing, but also for the confirmations, confidentiality, splitting of samples, etc. etc.

I hope I've been some helpful.

Take Care, Be Safe, God Bless,

Karen M.