Drug Testing - Drug Test Types
|
|
 |
Urine drug testing is the most common way to test for drugs. However
there are a number of different drug testing methods available and
sometimes the hair, saliva or perspiration may be drug tested.
To understand the principles behind
drug testing technology, some knowledge is required
about the
way in
which
the body
deals with chemical compounds such as drugs. Irrespective of the
method of intake, all drugs, pharmaceutical and otherwise, undergo
a series
of bio-chemical reactions in the body. These reactions release
the active compound and then gradually degrade the drug into slightly
different structures. These structures, also called metabolites,
are then excreted
from the body in a variety of ways. Urine is the main excretory
route
for drugs and their metabolites.
Urine Drug Testing
The following is a summary of the analytical methods used by laboratories
to detect the presence of drugs or their metabolites in urine.
Immunoassays
These tests are most commonly used to screen samples. In the event
that drugs or their metabolites are detected, then the sample
is normally tested again using an even more sensitive test such as
Gas Chromatography and Mass Spectometry. Immunoassays work on
the
principle of antigen-antibody interaction. Antibodies are chosen
which will bind selectively to drugs or their metabolites. The
binding is then detected using either enzymes, radioisotopes
or fluorescent compounds.
EMIT (Enzyme Multiplied Immunoassay Technique)
is manufactured by Syva Laboratories. It uses an enzyme as the detection
mechanism.
It is the cheapest, simplest to perform and the most widely used
of the immunoassays. Unfortunately, it is also the easiest to fail
and more worryingly, the least accurate: giving a
4-34% false positive
rate.
RIA (Radio Immunoassay) is manufactured by Roche
Diagnostics. It is similar to EMIT but uses a radioactive isotope
such as iodine instead of an enzyme. However, because it involves
using radioactive substances, it is less popular than EMIT. This
is a highly sensitive form of testing mainly used by the military.
FPI (Fluorescence Polarization Immunoassay) is manufactured by Abbott
Laboratories. Fluorescent compounds mark the selective binding of
antibodies to drugs and their metabolites. It is highly sensitive
and highly specific.
Thin Layer Chromatography
This procedure involves the addition of a solvent to the sample
causing the drugs and their metabolites to travel up a porous strip
leaving
colour spots behind. As each different substance travels a specific
distance, the strip can then be compared with known standards.
This test gives no quantitive information, it merely indicates
the presence of drugs or their metabolites. Furthermore, it relies
on the subjective judgement of a technician and requires considerable
skill and training. It is not widely used.
Gas Chromatography and Mass Spectometry
These are the most precise tests for identifying and quantifying
drugs or their metabolites in the urine. They are usually used as
a confirmation
test following a positive result on an Immunoassay. It involves
a two step process, whereby Gas Chromatography separates the
sample into its constituent parts and Mass Spectometry identifies
the
exact molecular structure of the compounds. The combination of
Gas Chromatography and Mass Spectometry is considered to be the
definitive method of establishing the presence of drugs or their
metabolites in the urine. However, the equipment necessary to
perform it is extremely expensive and this is reflected in the price
for
testing each sample. Occasionally problems do arise with poor
calibration of the equipment.
Although urine is most commonly tested, occasionally laboratories
use one of the following methods to detect the presence of drugs
or their metabolites:
Hair Testing
The technology behind the hair test was pioneered by Psychemedics
Corporation. When drug metabolites are circulated in the blood,
they enter the scalp's blood vessels and are filtered through
the hair.
These metabolites remain in the hair and provide a permanent
record of drug use. About 50 strands of hair are taken and dissolved
in
a series of solvents. The laboratory then analyzes the liquified
sample using Gas Chromatography and Mass Spectometry. This makes
it a highly sensitive test, yet the considerable cost and prolonged
process means that it isn't often used. It also usually requires
a confirmation drug test using urine.
Perspiration Testing
PharmaChem have produced a patch which is worn on the skin for a
period of time. The patch contains a mechanism which is able
to detect the presence of drugs or their metabolites as they are
excreted
in the individual's perspiration. The patch is used mainly to
monitor people on parole or probation.
Saliva Testing
Epitope have recently developed a test which detects drugs or their
metabolites in saliva. However, this sort of test is limited
to detecting very recent drug use. In one study, saliva testing was
only able to detect cannabinoids 4-10 hours after the subjects
had been smoking. It is likely that this test will be confined
to detecting current intoxication only.
Blood Testing
Although expensive and intrusive, blood testing is the most accurate
confirmation of drug use. Since blood testing accurately detects
the presence of the drug or its metabolites at the time of testing,
the results from this type of test are the best indication of
current intoxication. Blood testing for the use of drugs is primarily
used
in accident investigations or for health/life insurance medicals.
Cannabinoids can be detected up to six hours after consumption
by testing blood; after that, the metabolite concentration falls
rapidly, and cannabinoids are not detectable in the blood after
22 hours.
(Back to the Top)
|
