Drug Testing - False Positives
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In drug testing, a false positive is defined as a drug free sample
falsely being reported as showing positive for drugs. This can occur
for a number of reasons including: improper laboratory procedure, mixing
up samples, incorrect paperwork and passive inhalation. But the most
common cause of drug testing false positives are cross reactants. A
cross reactant is a substance which because of its similar chemical
structure
to a
drug or its metabolite can cause a false positive result.
The following
substances can cause cross reactivity on an Immunoassay screen but
are unlikely to be mistaken on a Gas Chromatography/Mass Spectrometry
test (for more information on these tests and others, visit the types
of test page):
Ibuprofen
Ibuprofen is a common pain reliever and anti-inflammatory which
even in low doses used to cause a false positive for marijuana/cannabis
on the EMIT test. The EMIT has been changed to use a different enzyme
to eliminate these drug test false positives.
But recent evidence suggests that Ibuprofen taken in very high doses,
along
with
other anti-inflammatories such as Naproxen will still interfere with
the EMIT test.
Decongestants and Cold Remedies
Phenylpropanolamine and ephedrine are both substances found in many
over-the-counter cold remedies. They can result in a drug test
false positive for amphetamines on the EMIT test. Antitussives, to
suppress
coughs, such as dextromethorphan and perylamine may cause a drug
test false positive
for opiates.
Anti-depressants
Aside from when this class of drugs is specifically tested for,
some of them including amitriptyline can test positive for opiates
for
up to three days after use. Even quinine in tonic water can also
cause a positive result for opiates.
Poppy Seeds
Poppy seeds which are usually found on bread contain traces of morphine
and can
lead to positives for opiates. Codeine, which is found in many
pain relievers, may cause a false positive for morphine or heroin
because of its similar chemical structure.
Antibiotics
Certain newly developed antibiotics including amoxicillin and ampicillin
have been reported to cause false positives for cocaine.
DHEA
This treatment developed for use by AIDS patients will cause a false
positive for anabolic steroid use.
Benzodiazepines
Diazepam may cause a false positive for PCP.
Enzymes
A small fraction of the population excrete large amounts of certain
enzymes in their urine which may produce a positive drug test.
The enzymes in question are endogenous lysozyme and malate dehydrogenate,
which according to research may run as high as 10% of positive
samples. Melanin
Melanin is the pigment which protects skin and hair from UV
light. It is also very similar in chemical structure to THC
(Tetrahydrocannabinol, the active component in cannabis) and
some data exists claiming it causes false positives for cannabis.
Unfortunately,
an equal amount of data suggests that there is no link whatsoever.
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