Do not assume that a negative drugscreen means that no drugs of abuse were used. Many drugs of abuse are not identified on standard urine drugscreening samples
Do not assume that a negative drugscreen means that no drugs of abuse were used. Many drugs of abuse are not identified on standard urine drugscreening samples: Excerpt from Avoiding Common Pediatric Errors
Author:
Michael S. Potter and Anthony Slonim, MD
What to Do - Interpret the Data
Like all diagnostic tests, it should not be assumed that a negative drug screen
indicates with perfect accuracy that no illicit drugs have been used by the
patient. Although rapid urine drug tests allow the quick detection of a wide
variety of drugs, there are other factors to consider when interpreting the
resultsofthesetests.Generalurinedrugtestsshouldonlybeusedasaninitial
screening mechanism for determining whether a drug of abuse is present in a
patient. More-specific drug tests should be considered after an initial screen
is performed and analyzed. A urine drug screen is most valuable when the
diagnosis is unknown, that is, when one is not certain whether symptoms
are being caused by drugs or by disease.
There are several techniques used for drug detection, including chromatographic methods,immunoassays, and chemical and spectrometric techniques. Chromatography is used for broad-spectrum analysis, whereas immunoassays are used for specific analysis. Being aware of what drug coverage
is available in particular toxicology screens is helpful. Most tests identify
analgesics, amphetamines, antidepressants, barbiturates, cocaine, ethanol,
and opiates. Drugs that are not commonly found in standard drug screens
include bromide, carbon monoxide, chloral hydrate, clonidine, cyanide,
organophosphates, tetrahydrozoline, colchicines, cyanide, iron, β-blockers,
calcium-channel blockers, clonidine, and digitalis. Note that traces of many
drugspersistforlengthsoftimethatmaynotbeclinicallyrelevantdepending
on the situation. Realizing that false-positive and false-negative results are
not uncommon is essential for making clinically sound decisions. As such,
confirmation analyses may be required. In addition, inquiring about the patient's legal drug use can help to clarify toxicology screening results. Aspirin
and acetaminophen, for example, are very common analgesic ingredients
in many medications, so measuring their prevalence should be considered
(Table 76.1).
When determining which specimen to collect for use in a drug screen,
note that urine is the best specimen for producing the highest rate of positive
findings among the greatest number of drugs when compared to gastric
aspirates or serum. Obviously, the earlier the urine is collected, the more
drugs can be detected because some drugs have short detection intervals.
Whenextraordinaryscreeningisavailable,addingabloodsampletotheurine
can produce a slightly higher yield of positives. Gastric aspirates frequently
contain high concentrations of parent drugs, which is helpful when a drug is
already metabolized to an appreciable extent and cannot be identified based
on urinary metabolites.
Being conscious of what drug tests are available at one's medical institution can help to properly diagnose suspected drug abuse-related illnesses.
Recognizing which drugs are commonly missed in routine drug screens and
which drugs—illicit or otherwise—result in false positives can also prevent
time-wasting, erroneous drug tests from being ordered (Table 76.2).
Suggested Readings
Ford MD. Acute poisoning. In: Goldman L, Ausiello D, eds. Cecil Textbook of Medicine. 22nd
ed. Philadelphia: Saunders; 2004, pages 328–40.
Jenkins RR.Substanceabuse.In: BehrmanRE,KliegmanRM, Jenson HB,eds. NelsonTextbook
of Pediatrics. 17th ed. Philadelphia: Saunders; 2004, pages 653–62.
Lee J. Poisonings. In: Robertson J, Shilkofski N, eds. The Harriet Lane Handbook: A Manual
for Pediatric House Officers. 17th ed. Philadelphia: Elsevier Mosby, 2005, pages 17–71.
Osterloh JD. Laboratory testing in emergency toxicology. In: Ford MD, Delaney KA, Ling LJ,
et al, eds. Clinical Toxicology. Philadelphia: WB Saunders Company; 2001.
Pictures
Book Source Details
- Book Title: Avoiding Common Pediatric Errors
- Author(s): Anthony D Slonim MD, DrPH; Lisa Marcucci MD
- Year of Publication: 2008
- Copyright Details: Avoiding Common Pediatric Errors, Copyright © 2008 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Avoiding Common Pediatric Errors
Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD
Publisher: Lippincott Williams & Wilkins
Copyright: 2008
ISBN: 0-7817-7489-6
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