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Q: False negative drug screen ( Answered 5 out of 5 stars,   8 Comments )
Subject: False negative drug screen
Category: Health > Medicine
Asked by: triciatx-ga
List Price: $20.00
Posted: 21 Jun 2005 08:57 PDT
Expires: 21 Jul 2005 08:57 PDT
Question ID: 535492
My husband in on 100% disability thru the V.A.  Without fail, he takes
prescription controlled release Oxycontin 2 times a day. The problem
is that he has had negative results on 2 urine drug screens.  He also
drinks beer daily and takes other prescription meds.  What could be
interfering with the drug screen and causing it to read a false

Request for Question Clarification by tutuzdad-ga on 22 Jun 2005 06:18 PDT
In order to answer your question we'd (at the very least) need to know
ALL the substances (legal or not) he is taking and exactly what type
of drug screen is being adminstered to him. Absent that, we can
speculate about the cause as an answer if you like; the choice is


Clarification of Question by triciatx-ga on 22 Jun 2005 14:07 PDT
He takes no illegal drugs...Opiates are what they are testing for to
insure that he is taking the oxycontin himself and not selling it,
etc.  He drinks coffee all morning and beer all afternoon until

The following drugs are what he takes:

Oxycontin CR 40 mg every 12 hours 
Oxycodone 5 mg twice a day as needed for breakthrough pain   
Lisinopril 20 mg every 12 hours
Hydrochlorothiazide 25 mg once a day
Flunisolide Nasal spray every 12 hours
Aspirin 81 mg once a day
Levobunolol Eye drops every 12 hours
Alphagarf 5% Eye drops every 12 hours
Metroprolol 25 mg every 12 hours
Felodipine 5 mg once a day
Citrucel Fiber once a day

Thanks for your help.
Subject: Re: False negative drug screen
Answered By: tutuzdad-ga on 22 Jun 2005 18:58 PDT
Rated:5 out of 5 stars
Dear triciatx-ga;

Thank you for allowing me an opportunity to answer your interesting
question. I am not a medically trained physician but I am a law
enforcement laboratory technician who routinely handles evidence
including specimens for drug screens.

A drug screen is a complex thing and the higher tuned (more sensitive)
it is the more complex it becomes. You see, drug screens can be
adjusted to detect various trace amounts of many different types of
drugs. Some test react positively for the presence of drugs
(substances or derivatives) only if those traces appear in the test
medium in certain volumes. For example, a person on parole may be
given a test for marijuana (cannabis, hash, etc) that will respond
positive if the test medium contains traces above  a certain ?cutoff
level? where the cutoff level is very low (10ng/ml possibly) . Whereas
a person applying for a job may be given a test for marijuana
(cannabis, hash, etc) that will respond positive only if the test
medium contains traces above a certain ?cutoff level? where the cutoff
level is very high (50ng/ml possibly).

It appears that one of a number of things have happened (and I am only
being objective now so don?t freak out on me here, ok?):

First possible scenario: Your husband is not taking his medicine or is
not taking it properly and the test is showing negative because he
doesn?t have enough Oxycontin and/or Oxycodone in his system to
trigger the cutoff level of the test.

Second possible scenario: Your husband really is taking his medicine
but the cutoff level for positive on the test that is being
administered to his specimen is unintentionally (or ignorantly) higher
than what is intended, therefore a negative result is being detected.
If this is the case then your husband is indeed positive, just not
positive ?enough? to read positive on this particular test.

Third possible scenario: The drug screen is being inappropriately or
incorrectly administered or the specimen is being fouled, switched or
tampered with (intentionally or not) between collection and

Fourth possible scenario:  The drug screen is being misinterpreted and
recorded incorrectly.

There is some recent history with false results as is evidenced by
studies conducted by the Veteran?s Administration (VA). For example,
the VAGLAHS Outpatient Pain Program (OPMP) utilizes a standard Drug of
Abuse (DOA) immunoassay and Biorad High Performance Liquid
Chromatography (HPLC) Remedi-HS. These tests are used to monitor for
medication compliance. In 2004  as many as 44 % of patients tested
were found negative for opiates despite patient prescribed opioid
medication. The VA concluded that the DOA test was not sensitive
enough (in other words the cutoff was too high to detect the presence
of opioids commensurate with what the VA considered minimum

The bottom line though is that the consumption of alcohol, as you seem
to be concerned about, has no effect on a drug screen for opiates. If
that were the case most illegal narcotics users would also be an
alcoholics to cover up his crime. You couldn?t keep enough beer in
stock to stay open more than 8 hours at a time if addicts thought for
a moment that beer fooled a drug screen. In addition I?ve been in law
enforcement more than 20 years now and I?ve never EVER heard of
alcohol messing up a drug screen; nor have I ever met an authority
that claimed so. I saw noting in my research that indicate the other
drugs your husband takes concomitantly can interfere with a drug

Not knowing a think about either of you more than you?ve told me, I?d
have to blindly suspect scenario #1 or scenario #2 (but I REALLY
suspect #2 the most likely cause). If the matter is a serious issue
with your husband, I recommend you go to your physician next time a
text is administered and also ask for blood to be drawn or some other
alternative testing method to show your are following the rules as you
are required to do.

I hope you find that my research exceeds your expectations. If you
have any questions about my research please post a clarification
request prior to rating the answer. Otherwise, I welcome your rating
and your final comments and I look forward to working with you again
in the near future. Thank you for bringing your question to us.

Best regards;
Tutuzdad ? Google Answers Researcher


HSR&D 2004 National Meeting Abstracts
?Result of Urine Toxicology in VA Patients Treated In a Pain Clinic?



Google ://


Drug screen



False negative

Clarification of Answer by tutuzdad-ga on 23 Jun 2005 19:04 PDT
Thank you ever so much for your generosity!

triciatx-ga rated this answer:5 out of 5 stars and gave an additional tip of: $20.00
Excellent research and report.  I was very impressed that a study was
included that was precisely on the subject of my question. 
tutuzdad-ga is great and I look forward to working with him/her again.

Subject: Re: False negative drug screen
From: isophist-ga on 22 Jun 2005 04:51 PDT
are you sure they're LOOKING for oxycontin in the toxicology screen?
it all depends on what the test is looking can totally miss
cocaine if it's only looking for marijuana...etc.
Subject: Re: False negative drug screen
From: rhenium-ga on 23 Jun 2005 03:35 PDT
Caffeine, alcohol and hydrochlorothiazide are all diuretics, and if he
drinks a lot of liquids he will flush the opiates from his system
faster, and the urine sample will become diluted.
Subject: Re: False negative drug screen
From: tutuzdad-ga on 23 Jun 2005 06:11 PDT
That is not true at all. The Parts per million can naturally diminish
over time but nothing can "dilute" a sample unless it is added to the
sample "after" collection. The problem is clearly the the
VA article.

Subject: Re: False negative drug screen
From: rhenium-ga on 23 Jun 2005 08:09 PDT
I still think you are wrong, diuretics speed up the elimination of
drugs excreted by the kidneys, and much more so if you consume larger
amounts of liquids (like beer).

A person using (multiple) diuretics and ingesting larger amounts of
water may have an unusually low urine opiate concentration, one that
falls below the cutoff-point on a drug test designed for "normal"
individuals to check for a relatively high opiate concentraton. How
many hours had passed from the last opiate dose to time the urine was

I may have used the term "diluted" wrong, tho... In chemistry, when
comparing two solutions with different concentrations, you usually
call the one with a lesser concentration "diluted".
Subject: Re: False negative drug screen
From: tutuzdad-ga on 23 Jun 2005 10:09 PDT
But the problem is that you are speculating that diuretics "speed up
the elimination of drugs excreted by the kidneys", when in fact the
diuretics taken by the patient may merely make him excrete liquids at
a medically "normal" rate where he was not doing so prior to being
prescribed the diuretics.

Subject: Re: False negative drug screen
From: rhenium-ga on 23 Jun 2005 11:32 PDT
It's much more likely that he is being prescribed the diuretic
medication against high blood pressure, caused in part by the alcohol
and caffeine he consumes, his regimen also includes other drugs for
treating high blood pressure.

Drug tests are not bulletproof, and my explanation fits your second
scenario. I find it likely that a test designed to make sure a patient
is using all his medication has a high cut-off point, the test is
useless if a patient can sell half of his dose to others and still
test positive.

(Just to make clear, I think you are an excellent researcher; everyone
can make oversights.)

Subject: Re: False negative drug screen
From: tutuzdad-ga on 23 Jun 2005 12:23 PDT
I tend to believe the test is not tuned correctly for this particular
result as evidenced by the VA article in which the author explains how
the reasons for the faulty results are not yet known but attributed to
a non-sensitive test. I deal with integrity issues with regard to
these types of samples daily in a lab environment so I don't see where
dilution is as issue.

At any rate the scenarios listed are the most likley. Which one
actually fits remains to be seen. Thanks for the positive vibes

Subject: Re: False negative drug screen
From: linezolid-ga on 08 Jul 2005 17:41 PDT
Re: diuretics
If you take a diuretic daily, your body equilibrates, reguardless of
what the diuretic is (or how many diuretics you take).  Over the long
term, the amount of liquid you excrete is matched by the amount of
liquid you ingest (minus insensible losses: breathing, sweating).
Otherwise, diuretics would kill people by dehydration, and quick. 
Diuretics will essentially maintain you at a lower effective vascular
volume (another topic entirely).

Re: fluid intake.
Assume that the amount of drug filtered per unit time follows first
order kinetics (the most common kind of secretion/excretion).  This
means that the blood concentration of the drug is related to the rate
of excretion.  The amount of urine is irrelevant to the amount of drug
excreted.  If during a given period (say between 2 and 4 hours after
your take your oxycontin) you excrete X miligrams of the drug, and you
produce 200 mililiters of urine, the concentration of drug in your
urine will be X/200 mg/mL.  If, the following day, you produce 400mL
of urine during the same period (between 2 and 4 hours after you take
your oxycontin), the concentration in your urine will be x/400 mg/mL,
or HALF the concentration it was during the same peroid the previous
day.  If the threshold for testing positive is set at x/300 mg/mL, you
will test positive on the first day, and negative on the second day,
despite having the same blood levels on both days.

Thus: both Rhenium and Tutuzdad are potentially correct.  The
threshold for testing is very likely contributing to the problem.  AND
the high fluid intake (coffee and beer) might possibly contribute. 
The diuretic effects of hydrochlorthiazide, ethyl alcohol, and
caffeine are irrelevant.


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