Urine Drug Screen False Positives

Urine drug screens aren't completely useless, but they have a number of limitations. Here is a table where I have compiled all of the false positive causing drugs I could find:



Update 4/22/2016:
Here are my sources:

I started with this paper which was I originally heard on EM Abstracts (Jan 2011):

Brahm NC, Yeager LL, Fox MD, Farmer KC, Palmer TA.
Commonly prescribed medications and potential false-positive urine drug screens.
Am J Health Syst Pharm. 2010 Aug 15;67(16):1344-50.
doi: 10.2146/ajhp090477

Special thanks to Jon Cole from Hennepin who made this fantastic video:

Other sources include:
UMHS Guidelines for Clinical Care May 2009

Standridge JB, Adams SM, Zotos AP.
Urine drug screening: a valuable office procedure.
Am Fam Physician. 2010 Mar 1;81(5):635-40.


Reisfield GM, Haddad J, Wilson GR, Johannsen LM, Voorhees KL, Chronister CW, Goldberger BA, Peele JD, Bertholf RL.
Failure of amoxicillin to produce false-positive urine screens for cocaine metabolite.
J Anal Toxicol. 2008 May;32(4):315-8.

Ly BT, Thornton SL, Buono C, Stone JA, Wu AH.
False-positive urine phencyclidine immunoassay screen result caused by interference by tramadol and its metabolites.
Ann Emerg Med. 2012 Jun;59(6):545-7.
doi: 10.1016/j.annemergmed.2011.08.013

Swift RM, Griffiths W, Cammera P.
False positive urine drug screens from quinine in tonic water.
Addict Behav. 1989;14(2):213-5.

And I Didn’t Know It

Inspired by Saurabh Jha:
Not exactly op notes, but some ED limericks I wrote:

Mr. Jones ate some bad guacamole
press on his belly, he shouts "holy moley!"
we did a CT
and what could it be?
then he went for a lap'r'scopic chole


Mrs. Smith was awoke from her nappy
her belly was feeling quite snappy
white count? twasn't high
a fever? tad shy…
but the CT, of course, showed an appy


there once was a man from Bologna
thought he had caught a touch of pneumonia
he seemed like whiner
and he got a d dimer
no PE; just some bad allodynia

Of course the cake goes to:

Roc vs Sux Revisited: Cochrane Update

I’m not going to reinvent the wheel, so a sweeping summary:
Traditionally, succinylcholine has been the paralytic of choice for RSI. However, succinylcholine can (rarely) lead to hyperkalemia, particularly in patients with chronic neurological problems.* Proponents of rocuronium for RSI suggest avoiding potentially fatal hyperkalemia by routinely using roc, summarized superbly by Reuben Strayer here. When dosed properly (1.2 mg/kg or higher), time of onset and intubating conditions are equivalent to between rocuronium and succinylcholine.

Defenders suggest that succinylcholine's shorter duration of paralysis is an advantage: if you can’t get the tube, the patient starts breathing. Unless the patient critically desaturates before return to an unparalyzed state:


Note the title of the source of this familiar graph: Critical Hemoglobin Desaturation Will Occur before Return to an Unparalyzed State following 1 mg/kg Intravenous Succinylcholine (Benumof, Dagg, Benumof. Anesthesiology. 1997 Oct;87(4):979-82.)

In the original 2008 Cochrane review, the authors (including Perry & Wells) find that time of onset and intubating conditions are inferior to succinylcholine… when dosed inadequately. Cochrane just released another update and reached the same conclusion with mostly same data, but again, note that when dosed appropriately, rocuronium is just as good as succinylcholine, with a p-value of 1.00.


Of course that’s only 86 patients dosed at 1.2 mg/kg, but the results were identical. The Cochrane authors further find that even some lower doses of rocuronium (down to 0.9 mg/kg) are just as good:


but then come to the same conclusion:

This is a bit odd. When I can’t intubate or ventilate a patient, they don’t nicely wake up in 9 minutes. In fact, more paralysis may even be preferred, particularly to optimize further attempts at mask ventilation, including EGD placement. And more importantly, to stop a panicking, suffocating patient from stopping me from stabbing them in the neck. But the bottom line is that if the succinylcholine has worn off, then they’ve probably already critically desaturated.

A number of Very Smart People (including Rob Huang, Minh Le Cong, Chris Nickson, and Reuben Strayer) have all pointed out that Cochrane is supposed to summarize the data, not editorialize:
There are some situations where I still reach for succinylcholine, primarly when I don’t want to lose my neuro exam for an extra half hour, mostly severe head trauma and status epilepticus. Also, if I can’t get a line or an IO and need to use IM drugs for RSI, rocuronium is probably too dilute.**

Ultimately, this isn't that big deal. Hyperkalemia is bad, but rare. But if we can avoid it without worsening time to onset or intubating conditions, why not?

My biggest problem with rocuronium? It comes in 50 mg vials. One*** great tip I learned from Reuben Strayer : when I ask a nurse for rocuronium, I always clearly specify that I need 2 (or 3) vials.

*Most of which are fairly rare and I (fortunately) don’t need to intubate very frequently. But when that relative zebra is really sick, I have enough on my mind and I don’t want to have to think to hard about which drugs may be dangerous. Note that in MG, you can use succinylcholine but have to use more; you can use a lower dose of rocuronium but a normal dose will just paralyze them longer, which is much safer than me having to remember this whole paragraph and do math when the chips are about to hit the fan.

**Bad day for everyone. Not ideal but I prefer to have my quiver more full than my diaper.

***One of too numerous to count. Read and watch everything at emupdates.com

Special thanks to Minh Le Cong & Reuben Strayer for their prepublication peer review.

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