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PROCEDURE
TITLE:
Test Information - Test Methods
Laboratory testing falls into three general categories. The following is a brief
description to provide a basic understanding of the limitations of each category. In general,
testing for drugs of abuse does not measure the actual drug present in the body. The human
body will break down drugs into various smaller compounds called metabolites. Most of the
metabolites are excreted into the urine, where they can be readily detected. Some will also
be present in the saliva, sweat and eventually the hair. See table below illustrating the
differences in sample types.
PRINCIPLE:
Qualitative Tests:
These are basic, almost "fool-proof" test devices, which yield simply a positive or negative result.
Such tests are useful when results are required as soon as possible. The manufacturer of such tests
designs them for use by individuals who are not trained in laboratory procedures. A common
example is the home pregnancy test. The "dipstick" provides a positive reading only when the HCG
hormone reaches a certain level, which indicates the pregnancy.
According to a 1999 Government study, these tests are at best about 85% accurate for the drugs of
abuse. There are several problems with qualitative tests. Accuracy levels will vary with the various
manufacturers, so some dipsticks may actually read lower than the customary cutoff, while others
may be a little higher. The amphetamine and opiate cut-off levels are higher on the dipsticks than
testing by TASCLabs. The Federal Department of Transportation established the higher levels to
allow greater compliance of transportation workers to random drug screens. (See Test Information Interpretation - Cut off Values) Thus, there will be more negative results seen as compared to
TASCLabs.
Qualitative tests, like semi-quantitative tests, are subject to interference by certain other substances.
Some over the counter medications contain drugs that are similar to the drugs of abuse. Certain
herbal products or foods might also yield a false-positive result. Careless collection or performance
of the dipstick test can cause negative results.
Semi-Quantitative Tests:
Semi-quantitative tests are more specific than the qualitative assays. They are performed in the
laboratory under controlled conditions. Test Instruments are calibrated with known standards and
checked with known controls, to ensure the results are accurate. Generally, the tests are about 95%
accurate. The term "semi-quantitative" is somewhat misleading, as numeric values are obtained,
which can be used to monitor the compliance of a client.
Semi-quantitative tests, like the qualitative tests work on the basis of an antibody - antigen reaction.
The antigen (drug metabolite) attaches itself to the antibody (test reagent) to produce a color. The
intensity level of the color is equal to the concentration of the drug metabolite. Usually all the
metabolites from a drug are detected as a group.
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The tests are subject to similar interference as are the dipstick tests. TASCLabs maintains a listing
of known substances that can or cannot affect the various tests. This listing is called the "Test
Effects Table" and is found in the TASCLabs Field Manual.
Quantitative Tests:
A quantitative assay is very specific and accurate for a given test. In the medical world, they are
used to adjust treatments and make life & death judgements of a patient. In the substance abuse
world, they can make the difference in deciding if a client is truly following their program or
attempting to abuse the system.
For Drugs Assays, this quantitative "gold standard" is the GC/MS (Gas Chromatography / Mass
Spectroscopy). This assay is capable of measuring each of the individual metabolites of a specific
group of drugs. (As compared to semi-quantitative, which measures all the metabolites.)
TASCLabs refers samples for confirmation to a Reference Laboratory for the quantitative GC/MS
test.
The semi-quantitative screening tests are always performed before requesting the confirmation test,
because the GC/MS assay uses solvents to extract the specific drug group metabolites. GC/MS
cannot be used as a screening system, because each drug group requires a different extraction
process, which is costly. Adulterants typically do not interfere with these assays.
INVALID TEST: Occasionally a confirmation test may be reported as invalid by the
Reference Laboratory. The laboratory may have protocols for certain drugs, as to which
metabolites are to be detected before designating the sample as positive. For example, the
most likely to have such a protocol is cocaine, as it is tested for three metabolites. If one
metabolite is below the cut-off level, the assay may be called invalid, because something is
interfering with the confirmation. If two of the three metabolites are below the cut-off, the
confirmation may be called negative. This does not apply to all drug groups as most have
only one or two major metabolites measured to be called positive.
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TASC Laboratories
Illustration of Sample Types:
Specimen Type:
Urine
Detection Time
Usually drug use within 1-3 days
Notes
Pro: Oldest and most common testing.
Most accepted by the court system.
Saliva
Detects usage earlier than urine by
about 4-6 hours.
Con: Sample collection issues or concerns
A person abstaining long enough can cause a
negative result.
Pro: Easiest sample collection.
Results equivalent to urine, but lower values.
Hair
Drug use over longer period. One
inch of hair is about 60 days
Con: Detection times are shorter than urine
Pro: Shows chronic use over longer period.
Sample easy to collect, store and ship.
Sweat
Eye
Sample gathered using a sweat
patch over a week or more to
evaluate usage.
Con: Testing takes longer and more expensive
Black hair shows higher concentration than
gray hair.
Pro: Detects usage over a longer period
User may have hard time abstaining for a long
period of time.
Eye movements are measured,
which is associated with drug
usage.
Con: Reports of external contamination being
absorbed into the patch giving false positives.
Pro: Quick evaluation, especially when large
number of persons to be tested.
Equipment relatively low cost.
Con: Not recommended for persons under
age 16 or over age 50
Fatigue can give false positives.
RELATED DOCUMENTS:



Test Information - General
Test Information - Result Interpretation
Test Information - Reporting
DOCUMENT APPROVAL:
Revision History:
Date
Rev. No.
11/15/02
0
04/30/04
1
874019097
William J. Salas BS, MT (ASCP), NM (ASCP) - Laboratory Director
(Original signed document maintained in Master Laboratory Manual)
Change Description:
Original Document created
Removed section from General Info and added table
illustrating sample types.
Eff: 04/30/04
Doc. No. 09.007
Author:
Bill Salas
Bill Salas
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