American Society of Regional Anesthesia and Pain Medicine November 2017 - 29

relatively inexpensive (Medicare midpoint of $20.22-$107.85),7
whereas confirmatory mass-spectrometry-based methods have a
higher analytical sensitivity and specificity, incurring much higher
costs (Medicare midpoint of $158.98-$343.07).7 Clinicians must
know which drugs are tested in the particular panel ordered.
In fact, the term "drug screen" is a misnomer because it suggests
that it detects all drugs in a given class. For example, the common
immunoassay for the detection of opiates uses an antiopioid
antibody that detects morphine and will show positive if a patient
is taking morphine, codeine, or heroin. The test may or may not
detect semisynthetic opioids (such as hydrocodone and oxycodone)
and will not detect synthetic opioids (such as buprenorphine and
fentanyl). Hydrocodone is the most commonly prescribed opioid in
the United States, yet the opiate screen may be considerably less
sensitive for this drug. In a
review of urine specimens
with unexpected negative
opiate immunoassay results
in hydrocodone users, 72.3%
were found to be positive for
hydrocodone or its metabolite
using confirmatory testing.8

with the semisynthetic medications. The test would have come
back as positive, giving no insight that the patient was not taking
oxycodone. There are immunoassays designed to detect specific
semisynthetic opioids, but those are not typically included in the
basic screens. The immunoassay specifically for oxycodone and
its metabolite, oxymorphone, has a sensitivity and specificity of
approximately 99%.9
In the United States, we are enveloped in a crisis where overdose
from opioids is the leading cause of accidental death.10 Although
we hope to see a decrease in prescribing opioids, it is important
that we do not let the pendulum swing back to the practice of
reserving opioids for end-of-life care. It is essential for physicians
who prescribe opioids to monitor their patients closely and identify
signs and symptoms of misuse and abuse. UDSs give unbiased and
reproducible objective data
and are an important tool in
the setting of addiction and
pain management. Although
numerous guidelines
recommend UDSs for pain
management patients as a
tool to monitor compliance,
there is a lack of specific
recommendations for
which to order and at what frequency. Therefore, clinicians must
understand the capabilities and limitations of assays performed to
prevent incorrect interpretation.

"With the growing epidemic, providers
must effectively monitor the use of
prescription opioids to identify misuse,
addiction, and diversion."

For the patient presented,
the mass-spectrometry screen was positive for oxymorphone and
negative for oxycodone. Oxymorphone is a metabolite of oxycodone
and is expected in the UDS of a patient taking oxycodone, although
the opposite is not true; that is, this patient is taking oxymorphone
and not taking the oxycodone as he stated. He was prescribed 150
tabs per month, states he takes one to two per day, and has only a
few tabs left. The numbers and the UDS do not add up, raising the
suspicion for misuse or diversion. In addition, the morphine screen is
positive. The common reflex is to assume he is taking nonprescribed
or illicit substances; the level of morphine detected is consistent with
the use of morphine, heroin, or ingestion of poppy seeds. In this case,
accusing the patient of using nonprescribed or illicit substances may
be wrong-unfortunately, there is no way to differentiate. Because of
the oxycodone discrepancy, the clinical decision was to wean opioids.
For the same patient, if a basic opiate immunoassay screen were
done, the interpretation of the results may have resulted in a very
different outcome. The benefit of the opiate immunoassay is that it is
rapid, sensitive, widely available, and relatively inexpensive. A major
disadvantage is that semisynthetic opioids may not be detected,
making the interpretation of compliance nearly impossible. The opiate
immunoassays perform very well when compared to confirmatory
screens in evaluating morphine; however, the cross-reactivity varies
among manufacturers for oxycodone and oxymorphone.9
In this case, the opiate may have been positive because of the
presence of morphine or because of the minor cross-reactivity

Answer: D
REFERENCES
1.

Volkow ND. America's addiction to opioids: heroin and prescription drug abuse.
The National Institute on Drug Abuse: Senate Caucus on International Narcotics
Control. Available at: https://www.drugabuse.gov/about-nida/legislativeactivities/testimony-to-congress/2016/americas-addiction-to-opioids-heroinprescription-drug-abuse. Published May 14, 2014. Accessed September 8,
2017.

Chen KY, Chen L, Mao J. Buprenorphine-naloxone therapy in pain management.
Anesthesiology 2014;120(5):1262-1274. doi: 10.1097/ALN.0000000000000170

Dowell D, Haegerich TM, Chou R. CDC guideline for prescribing opioids
for chronic pain-United States, 2016. JAMA 2016;315(15):1624-1645.
doi:10.1001/jama.2016.1464

Tenore P. Advanced urine toxicology testing. Journal of Addictive Diseases
2010;29(4):436-448. doi: 10.1080/10550887.2010.509277

Reisfield G, Bertholf R, Barkin R, Webb F, Wilson G. Urine drug test interpretation:
what do physicians know? J Opioid Manag 2007;3(2):80-86.

Starrels JL, Fox AD, Kunins HV, Cunningham CO. They don't know what they
don't know: internal medicine residents' knowledge and confidence in urine
drug test interpretation for patients with chronic pain. J Gen Intern Med
2012;27(11):1521-1527. doi: 10.1007/s11606-012-2165-7

Centers for Medicare and Medicaid Services. Clinical laboratory fee schedule.
Available at: https://www.cms.gov/Medicare/Medicare-Fee-for-ServicePayment/ClinicalLabFeeSched/index.html. Accessed June 15, 2017.

American Society of Regional Anesthesia and Pain Medicine
2017

https://www.drugabuse.gov/about-nida/legislative https://www.cms.gov/Medicare/Medicare-Fee-for-Service

Table of Contents for the Digital Edition of American Society of Regional Anesthesia and Pain Medicine November 2017