False Positive Drug Tests

[docB]

I had a pt today who was altered, combative, drunk and positive for amphetamines. Typical pt for me but this guy is on Artane. I started wondering if he might have Tourrett's or something and maybe that is why he was so whacked out. I was also wondering if the + amphetamine could be due to the Artane. Ritalin can give you a + amphetamine with some tests. It seems like I'm always trying to figure out what will and won't show up on a drug screen. Methadone won't turn a test + for opiates and some benzo (is it Klonopin?) wont trip the benzo test. Does anyone have a good way to deal with these other than just not getting them?

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[Hernandez]

As a lowly second year student, take my advice for what's worth, but my other degrees are in chemistry and I did quite a bit of reading into the specificity of the testing methods used for drug testing for a family friend (not what you?re thinking). And I stayed at a holiday inn express last night.

The best thing to do is use the medications you think are required to achieve the desired outcome, and just notate appropriately in the charts. I say this, because there is no universal standard operating procedure or testing method used for drug testing and not all tests have the same specificity,

The long story made sort is it all depends on which type of test kit/instrumentation is used. While methadone does not test pos. for opiates most of the time, some tests can return positives (especially the quicker tests), same thing with darvocet (propoxyphene) which is structurally related closer to methadone (being a synthetic opiate) can also test opiate positive. So it?s a compromise between to speed/reliability/cost effectiveness/repeatability.

So there is no easy way that I know of to get around these complications, in the end we're just going to have to just rely on pts. histories and the law to sort out everything else when needed.

 

[ERMudPhud]

We keep a printout from the test manufacture at one of the desks in the ED that lists all the cross reactivities. The one that killed me was a tricyclic test that our lab runs whenever we order our "serum tox" which in my mind should just be salicylate and tylenol levels. I gave up getting the clerks to just order those two and live with the bonus tricylic level. Unfortunately it cross reacts with damn near everything and even if it is detecting a tricylic the level is meaningless

 

[docB]

The one that killed me was a tricyclic test that our lab runs whenever we order our "serum tox" which in my mind should just be salicylate and tylenol levels.

What kills me at my houses is that there are these "order sets" that must date back to the era of Galen. They don't have lots of stuff that I do want and they include stuff I don't care about. I have trouble remembering what's in them because it's different at each hospital. Consequently I usually order my w/us piece meal which annoys the clerks. Can't win for losing.

 

[margaritaboy]

Klonopin frequently won't be positive for benzos, and methadone, fentanyl, and meperidine don't show up as positive for opiates. Finally, pseudophed and ephedrine (along with a lot of other stuff) cross react with amphetamines. At least this is true for our UDS assay.

 

[docB]

Klonopin frequently won't be positive for benzos, and methadone, fentanyl, and meperidine don't show up as positive for opiates. Finally, pseudophed and ephedrine (along with a lot of other stuff) cross react with amphetamines. At least this is true for our UDS assay.

So if you have a pt who fits the bill and a + UDS do you put "amphetamine abuse" as a diagnosis? I guess I could say "suspected amphetamine abuse."

 

[Sessamoid]

So if you have a pt who fits the bill and a + UDS do you put "amphetamine abuse" as a diagnosis? I guess I could say "suspected amphetamine abuse."

If by "fits the bill" you mean admits to amphetamine use, then yes. Otherwise, no. With as many false positives as you get on amphetatmines for most commercial urine drug screens, I don't diagnose that unless they admit to it personally. I had a friend of mine who tested positive for one of those crappy tests, even though she was clean as a whistle (very all-natural chick). Thing is, she was the top ranked modern pentathete in the world at the time, and missed her chance at the world championships because of it. Turns out one of the natural endorphins her body produces was cross-reactive. Sucks to be banned for two years for a faulty test.

 

[Cowboy DO]

And I stayed at a holiday inn express last night.

That was awesome. I just got soda up my nose. Thanks 🙂

 

[margaritaboy]

So if you have a pt who fits the bill and a + UDS do you put "amphetamine abuse" as a diagnosis? I guess I could say "suspected amphetamine abuse."

Not really sure. If everything fits and other clinical evidence exists, then I guess you could. Too many things cross react with amphetamines on our UDS for me to use it strictly as a screen for a diagnosis. Learning about the limitations of some of the assays in the UDS has made me question its utility and use in some cases. On the other hand the cocaine and PCP assays are pretty specific, and an isolated UDS finding could be enough.

Just one man's opinion.

 

[Seaglass]

Not to knock medical students, because I was the same way once (like 8 weeks ago), but I love it when you present a tox case to them and ask them what they would do and immediately they say "get a 'tox panel'" or 'tox screen.' Then I have a good time explaining that nothing worthwhile is actually tested for on the UDS and that you need to be able to get a good history and recognize toxidromes.

Speaking of toxidromes, had a good case of benadryl OD the other night. I had to travel down to the ED to read up on it since we don't have any tox references up here on the floors.

 

[Apollyon]

Speaking of toxidromes, had a good case of benadryl OD the other night. I had to travel down to the ED to read up on it since we don't have any tox references up here on the floors.

People go on and on about PDA's (and not the social kind), but I always have my Tarascon books in my pocket, no matter what service (the pharmacopoeia, Adult EM, and IM/Critical Care). The EM one has a page on toxidromes that focuses right in. I don't recall an off-service rotation I've been on when I didn't use them.

 

[Sessamoid]

People go on and on about PDA's (and not the social kind), but I always have my Tarascon books in my pocket, no matter what service (the pharmacopoeia, Adult EM, and IM/Critical Care). The EM one has a page on toxidromes that focuses right in. I don't recall an off-service rotation I've been on when I didn't use them.

I was in that boat until Epocrates matured. And then Skyscape came out with their 5 Minute Emergency Consult, at which point I dumped all those little books and pieces of paper forever. Add in Pepid, and I rarely even have to bother looking things up in textbooks at work anymore, as it's all in my scrubs pocket. No combination of little paper references can even come close to matching even a couple of those references anymore.

 

[grouptherapy]

the advantage of a pda is it doesn't elicit an adverse reaction from a patient like a booklet does. whip out a book and they tend to get nervous