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How
Drug Screens Are Performed
The aims of the drug screen
are to detect the presence of frequently abused drugs in the
urine of human subjects. Drug screens are used for one of three
purposes:
- medical purposes (e.g.,
to monitor a patient's progress in a medical treatment program
for a drug abuse problem the patient has acknowledged)
- legal purposes (e.g.,
to determine if a suspect had taken controlled substances
prior to some accident or crime)
- medicolegal purposes
(e.g., in an employer's drug abuse program aimed at both preventing
drug-related accidents and crimes and identifying and treating
employees with drug abuse problems).
For medical purposes, laboratories
often use simple, less-expensive methods aimed at identifying
specific drugs with which the patient has had problems in the
past. It is not expected that the results of such drug tests
will be used as evidence against the patient in court. If these
results are used as evidence, it is likely that defense testimony
will successfully impugn the evidence.
For legal and medicolegal
purposes, more stringent testing is necessary to obtain information
that will successfully withstand technical criticism in court.
Therefore, drug screens done for these purposes often take a
two-tiered approach. First, there is a screening test done on
the subject's urine. This is usually a sensitive test that may
have some discrepancies in specificity (for instance, some popular
over-the-counter cold medicines may yield a positive amphetamine
screen). Only if this test is positive for one or more drugs
is the second, more expensive test performed. Generally courts
will uphold testimony based on a drug test if positive results
were obtained on two separate tests based on different chemical
methods.
Amphetamines
Examples: amphetamine sulfate,
dextroamphetamine (Dexedrine), methamphetamine (Desoxyn, Methedrine).
Medical uses: Attention
deficit disorder (hyperactivity) of childhood, narcolepsy, obesity
(occasionally and for limited period)
Effects attractive to abuser:
Euphoria, increased ability to concentrate, increased alertness,
heightened ability to perform intellectual and physical tasks,
appetite suppression (for weight loss).
Adverse effects: Insomnia,
restlessness, irritability, palpitations, rapid heartbeat, sweating,
dilation of pupils, confusion, psychosis, convulsions, death.
How abused: Pills taken
orally; solution injected intravenously; occasionally snorted
into the nose in granular form.
Typical urine detection
cutoff level: 300 ng/mL
Period detectable after
last dose: Up to 30 hours on low dose, 120 hours on high dose.
Substances causing false
positive results (on initial drug screen only): decongestants
(ephedrine [Vatronol, Efedron], phenylpropanolamine [Propagest,
Sucrets Decongestant Formula, Rhindecon]); "diet pills"
(phenmetrazine [Preludin], phentermine [Phentrol, Tora, Fastin,
Obe-Nix, Obephen, Obermine, Obestin, Parmine, Phentamine, Phentrol
2, Unifast, Wilpowr, Adipex-P, Dapex-37.5, Ionamin, Phentrol],
phenylpropanolamine [Diadax, Prolamine, Control, Dex-A-Diet,
Dexatrim-15, Unitrol, Maximum Strength Acutrim, Appedrine];
blood vessel dilators (isoxuprine [Vasodilan], nylidrin [Adrin,
Arlidin]). Only confirmatory testing of the urine will determine
if these interfering drugs are present. It should be noted that
some of these drugs, such as phenmetrazine and phentermine,
while not technically amphetamines, have similar abuse potential
and similar adverse effects.
Phenylethylamine (a product
of decomposing, unpreserved urine) may produce false-positive
screens in unrefrigerated, old specimens which have not been
treated with fluoride preservative.
Barbiturates
Examples: Long acting-
phenobarbital; intermediate-acting- amobarbital (Amytal), butabarbital,
talbutal; short-acting- secobarbital (Seconal), pentobarbital
(Nembutal).
Medical uses: Treatment
of insomnia (short term only, and avoided altogether by most
physicians), long-term treatment of epilepsy (phenobarbital),
surgical anesthesia.
Effects attractive to abuser:
Sedation, loss of inhibitions, induction of sleep. Generally,
the short-acting barbiturates have more abuse potential than
long-acting types.
Adverse effects: Agitation,
confusion, nightmares, hallucinations, lethargy, hangover, suppression
of breathing reflexes, coma, death. Physical dependence is well
known, and withdrawal effects can be severe and dangerous, even
fatal.
How abused: Pills taken
orally; solution injected intravenously.
Typical urine detection
cutoff level: 300 ng/mL
Period detectable after
last dose: long-acting 7 days, intermediate-acting 2-3 days;
short-acting 1-2 days.
Substances causing false
positive results: None reported.
Methadone
Examples: Roxane, Dolophine
Medical uses: Treatment
of opiate addicts in approved program
Effects attractive to abuser:
Same as opiates (below)
Adverse effects: Same as
opiates (below) but with lesser degree of physical dependency
(addiction)
How abused: Pills taken
orally; solution injected intravenously.
Period detectable after
last dose: 7.5-56 hours
Substances causing false
positive results: doxylamine [Unisom Nighttime Sleep Aid]. Presence
of this substance would be ruled out by confirmatory testing.
Opiates
Examples: Morphine, heroin,
codeine (as found in many prescription cough medicines, such
as Robitussin-AC, and pain medications, such as Tylenol #3,
Phenaphen #3 & #4, Empirin #3 & #4), oxycodone (Percodan),
hydromorphone (Dilaudid), hydrocodone (as in many prescription
cough medicines).
Medical uses: Relief of
moderate to severe pain, treatment of persistent cough (codeine),
treatment of diarrhea.
Effects attractive to abuser:
Euphoria, sedation.
Adverse effects: Drowsiness,
apathy, confusion, nausea, vomiting, suppression of breathing
reflexes, constricted pupils, physical addiction, coma, death.
How abused: Pills taken
orally; solution injected intravenously or subcutaneously; occasionally
snorted into the nose in granular form.
Typical urine detection
cutoff level: 300 ng/mL
Period detectable after
last dose: heroin, 1-4 days; meperidine, 4-24 hours; morphine,
84 hour minimum
Notes: This family of drugs
undergoes extensive chemical changes due to the normal detoxification
processes of the body. Therefore, the drug detected in the urine
screen may not be the same as that originally taken by the subject.
For instance, both heroin and codeine are converted to morphine
before excretion in the urine.
Substances causing false
positive results: none reported; however, foods containing poppy
seeds (the natural source of traditional opiate drugs) will
produce true positive results when screening the urine of an
otherwise innocent subject.
Benzodiazepines
Examples: Diazepam (Valium),
chlordiazepoxide (Librium), flurazepam (Dalmane), oxazepam (Serax),
lorazepam (Ativan), clonazepam (Clonopin).
Medical uses: Treatment
of anxiety disorders, convulsions, and muscle spasms.
Effects attractive to abuser:
Euphoria, sedation, relief of anxiety, induction of sleep.
Adverse effects: Drowsiness,
apathy, fatigue, decreased activity level, dizziness, fainting,
impaired ability to concentrate on tasks, disturbance of vision
and hearing, physical addiction.
How abused: Pills taken
orally.
Typical urine detection
cutoff level: 300 ng/mL
Period detectable after
last dose: around 2-4 days, but depending greatly on dose. For
instance, a single 10 mg PO dose of diazepam may not ever be
detected, but a 5 times daily dose of 10 mg will be detectable
for 3-7 days.
Substances causing false
positive results: none reported.
Cannabinoids
Examples: Marijuana, hashish,
hash oil
Medical uses: Treatment
of nausea and vomiting due to cancer chemotherapy.
Effects attractive to abuser:
Euphoria, intensified sensual and aesthetic perceptions.
Adverse effects: Paranoia,
panic, impairment of memory and ability to perform tasks, distorted
perception of time, physical and psychological dependence.
How abused: Smoked in cigarettes
or pipe; occasionally eaten as ingredient baked into confections.
Typical urine detection
cutoff level: 100 ng/mL or 20 ng/mL (optional)
Period detectable after
last dose: This is highly variable. A one joint per week user
has detectable levels of cannabinoids form 7 to 34 days, while
a heavy daily user may be detected from 6 to 81 days after last
use.
Substances causing false
positive results: none reported. A screen detection cutoff level
of 20 ng/mL, requested by some laboratory clients, may produce
false positives due to passive inhalation of marijuana smoke,
but this is controversial.
At the cutoff level of
100 ng/mL, persons exposed passively to the smoke of others
by virtue of being in the same room with abusers should be negative
on urine drug screen, although more sensitive chemical techniques
(such as gas chromatography/mass spectrometry, which has a sensitivity
of 10 ng/mL) may demonstrate the drug in such an individual's
urine.
Cocaine
Examples: Cocaine hydrochloride
is the typical form used by abusers who ingest the drug by snorting
the granular form into the nose; it can also be dissolved in
water and injected intravenously. Cocaine base is available
in a waxy cake form ("rock" or "crack")
which is vaporized with a torch and the vapors inhaled through
a tube.
Medical uses: Used almost
exclusively by ear, nose and throat doctors to produce local
anesthesia and control blood loss during minor nasal surgery.
Effects attractive to abuser:
Euphoria, increased ability to concentrate, increased alertness,
heightened ability to perform intellectual and physical tasks,
sexual stimulation, heightened sociability, enhanced self-confidence.
Adverse effects: Restlessness,
nervousness, tremor, convulsions, disturbances in heart rhythm,
psychological dependence, myocardial infarction, sudden death.
How abused: Snorted, injected,
or smoked (see above).
Typical urine detection
cutoff level: 300 ng/mL
Period detectable after
last dose: 8-48 hours
Note: The laboratory detection
of cocaine is performed by analyzing the urine for the presence
of benzoylecgonine, a substance produced by the body's chemical
detoxification of cocaine. Continuous conversion of cocaine
to the metabolite occurs in voided, standing urine specimens
(even with fluoridation and refrigeration) unless the specimen
is kept at acid pH (<5). This may give the appearance of
a negative specimen "turning positive" during storage,
if the initial level of the metabolite was too low to trigger
the screen in the fresh specimen. In truth, the specimen was
positive all along, of course.
Substances causing false
positive results: none reported; however, some legal South American
herbal teas may contain small amounts of coca leaf extract,
which may trigger a positive test in an "innocent"
subject. Please note that cocoa, cacao, and Coca Cola are all
completely unrelated to coca, which is the source of cocaine.
Methaqualone
Examples: Quaalude, Sopor
Medical uses: Once used
as a sleeping pill/sedative, now methaqualone is virtually never
used for medical purposes.
Effects attractive to abuser:
Same as that for barbiturates (see above)
Adverse effects: Same as
that for barbiturates (see above)
How abused: Pills taken
orally.
Typical urine detection
cutoff level: 300 ng/mL
Period detectable after
last dose: up to 90 hours, depending on dose
Substances causing false
positive results: none reported.
Phencyclidine
Examples: PCP, "angel
dust"
Medical uses: Veterinary
tranquilizer; not used in human medicine.
Effects attractive to abuser:
Hallucinogenic effects
Adverse effects: Lethargy,
loss of co/rdination; unpredictable psychosis, sometimes with
criminally violent behavior; death.
How abused: Taken orally,
smoked in cigarette (often mixed with marijuana), injected intravenously
as a solution, snorted into the nose in granular form.
Typical urine detection
cutoff level: 75 ng/mL
Period detectable after
last dose: 5-10 days
Substances causing false
positive results: Thioridazine (Mellaril), an antipsychotic
drug, has been reported to cause false positive results, as
has the insecticide parathion.
Propoxyphene
Examples: Darvon, Dolene,
Doxaphene, Profene 65
Medical uses: Relief of
mild to moderate pain.
Effects attractive to abuser:
Same as that for opiates (see above)
Adverse effects: Same as
that for opiates (see above).
How abused: Pills taken
orally; occasionally injected as solution made by dissolving
pills in water.
Period detectable after
last dose: 1-3 days
Note: Propoxyphene is technically
an opiate and is chemically closely related to methadone. As
a pain-relieving drug, it is two-thirds as potent as codeine.
Although considered something of a minor leaguer in the opiate
world, it is nevertheless a cause of many drug-related deaths
(including that of former football star John Matuszak) especially
if used in combination with alcohol and other drugs.
Substances causing false
positive results: Methadone (see above) at high, toxic concentrations
may cause false positive results. Confirmation testing will
eliminate interference by this drug.
Alcohol
(Ethanol)
Examples: Beer, wine, distilled
spirits
Medical uses: Rarely, if
ever, used for medical purposes.
Effects attractive to abuser:
Release of social inhibitions, euphoria, sedation
Adverse effects: Same as
that for barbiturates (see above). Also, use by pregnant women,
even in small ("social") amounts may have adverse
effect on the fetus.
How abused: Drunk in beverage
Period detectable after
last dose: 8-10 hours
Note: Alcohol is the only
drug of abuse (other than tobacco) that is legal for all adults
to use. Illegal use (as in driving while intoxicated) is defined
by the presence of a blood alcohol level of greater than 100
mg/dL (0.10% by volume) in Texas (lower in some other states).
It is impossible to determine if a subject is legally intoxicated
by measurement of the urine alcohol level.
A blood specimen must be
collected for this determination to be made by a clinical laboratory.
Limitations
Of Drug Screens
From a practical viewpoint
it is impossible to determine in every case that a given individual
is impaired in the workplace due to drug abuse. Just as in the
case of alcohol, the use of drugs spans a wide spectrum of behavior,
from the occasional recreational user who assiduously avoids
coming to work under the influence, to the hard-core addict
whose only motivation is the acquisition of his or her next
dose. Generally the clinical laboratory is not able to distinguish
these two types of individuals. Such a distinction comes about
only by careful evaluation by professionals specially trained
in the psychology and physiology of drug abuse. The laboratory
should be used only as a helpful tool for such professionals.
Urine drug screens panels
are set up to analyze urine for a variety of drugs that are
known to have high abuse potential and affect task performance.
To rule out the presence
of all drugs that may impair a worker's performance is not generally
allowable within the bounds of cost containment. Certain drugs
which are not usually picked up on routine drug screens are
noted below. If intoxication by any of the drugs listed below
is suspected, it is recommended that the client contact the
B&A pathologist, who will be glad to help determine a strategy
as to how the case should be most efficiently handled.
Methylphenidate (Ritalin),
phentermine (Fastin, Parmine), phenmetrazine (Preludin), phendimetrazine
(Plegine), diethylpropion (Tenuate), mazindol (Mazanor, Sanorex),
benzphetamine (Didrex) and fenfluramine (Pondimin) all have
amphetamine-like effects and abuse potential. Some of them,
such as phentermine, benzphetamine, fenfluramine and diethylpropion,
may not be picked up on routine screens.
Methylenedioxyamphetamine
(MDA, "Ecstasy") is has been popular in Houston high
schools. Although it is technically an amphetamine, it requires
a special analysis to be identified.
Lysergic acid diethylamide
(LSD) is also chemically related to the amphetamines, but it
is much better known for its profound hallucinogenic effects.
Special analysis is available.
Meperidine (Demerol) and
pentazocine (Talwin) have physiological effects and abuse potential
essentially identical to those of opiates. However, since they
are chemically dissimilar to morphine, they may not show up
as "opiates" on a routine screen. Special analysis
is available.
Barbiturates which are
not easily detected on drug screens include amobarbital (Amytal),
pentobarbital (Nembutal), and butethal. The detection systems
used to pick up barbiturates are optimized for secobarbital
(Seconal), which is probably the most important barbiturate
in abusing populations.
Flurazepam (Dalmane), a
benzodiazepine used as a sleeping pill, is not ordinarily picked
up on benzodiazepine screens.
Glutethimide (Doriden),
ethchlorvynol (Placidyl), meprobamate (Miltown, Equanil), methyprylon
(Noludar), and ethinamate (Valmid) are sedative drugs that can
produce dependence and impaired function. Although they may
have some effects similar to those of the barbiturates, they
are chemically unrelated and must be detected with special procedures.
Hydrocarbon solvents. These
are inhaled by glue sniffers to produce a euphoric effect. Although
this seems to be less of a problem socially now than in previous
years, special analysis of hydrocarbons and chlorinated hydrocarbons
is available.
Ketamine (Ketalar), chemically
related to phencyclidine (PCP), is used as a general anesthetic
but has been abused, often by health care workers. It must be
injected for effect. Analysis is available only through specialized
laboratories, and turnaround time is typically long.
Designer opiates. These,
like meperidine, are synthetic analogues of natural opiates.
Accordingly, their chemical structure may be so alien to that
of natural opiates that they go completely undetected. These
are medically very significant drugs. For instance, 3-methylfentanyl
("China white") is 3000 times as potent as morphine
and has been responsible for over 100 overdose deaths in California.
Another, 1-methyl-4- phenylpropionoxypiperidine (MPPP), may
be contaminated with an unintended byproduct (1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine,
or MPTP) which destroys the substantia nigra of the brain and
produces permanent parkinsonism.
Adulteration of urine samples
with such substances as lemon juice, vinegar, chlorine bleach,
and NaCl has been used to successfully interfere with detection
of cannabinoids. Also, marked overhydration of the subject (by
quaffing large volumes of water) may so dilute the urine that
the concentration of the telltale metabolite falls below the
detection threshold of the screen.
A
Word On Test Reliability
Published data indicate
that a system of drug screening similar to that used by most
laboratories has a sensitivity of 76% and a specificity of 99%.
This excellent specificity parameter means that of 100 persons
who do not use drugs, 99 would be expected to test negative
by confirmation. This is certainly an excellent specificity
for any medical determination. However, one should also be aware
of another parameter, the predictive value of a positive test.
As applied to drug testing, this figure expresses the probability
that a subject that has tested positively has in fact used the
drug. Although a high specificity, such as 99%, optimizes the
predictive value, a more significant factor is the prevalence
of drug use in the population being tested. The more prevalent
the usage of drugs in a subject population, the greater the
reliability of drug testing procedure. Given the sensitivity
and specificity values quoted above, the following table indicates
the predictive value for several levels of drug abuse prevalence.
Therefore, in a population
with a high incidence of drug use (200 per thousand), the false
positive rate on drug screens is only 5%, while in a low-incidence
population (1 per thousand) the false positive rate on randomly
screened individuals (i.e., those of whom there is no particular
suspicion of drug use) is expected to be a whopping 93%! For
this reason, it is my recommendation that drug screens not be
applied on a random, not-for-cause basis, except in situations
where the prevalence of drug use is known to be high (such as
in substance abuse treatment programs).
Distributions restrictions:
This monograph may be freely duplicated and reformatted, as
long as the informational content is not altered. It may be
freely distributed, if 1) the author is given credit, and 2)
it is not used as an aid for marketing or maintaining commercial
laboratory accounts without prior express written permission
of the author
Copyright (C) 1989, 1993,
Edward O. Uthman
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