Rapid Tests
Rapid test = rapid lateral flow
test = immunochromatographic assay is a common test device in point of
care/point of collection (POC) testing (POCT).
How do rapid tests work/how do
rapid drugs tests/pregnancy tests work?
 Rapid
test is a lateral flow type of immunoassay used in rapid drug test, or drug
screen test. The immunoassay reagents are embedded at different sections of a
porous test strip. When a liquid sample is introduced to a sample zone of the
strip (usually at one end of the strip), the sample wicks towards the opposite
end of the strip, which results in the sample solution mixes with the assay
reagents and the analyte reacts with the reagents. At
the end, a color band of the color labeled reagent will be present or absent at a middle section of the assay strip,
which indicates the presence or absence of the analyte in the sample solution.
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What are the test procedures
using rapid tests?
The rapid test procedures are very
simple. The test sample is introduced to an end of the test strip by pipetting, dipping,
or other methods. Cassettes, cups (CupLab), dipcards (CardLab) are designed for
convenience. The rapid test results are visually read and no instrument is needed. The
lateral flow test result takes only 5-10 minutes to develop. Therefore, rapid tests are
suited in point of collection (POC) testing. Many rapid test products have been
approved by the FDA for non-professional/home use, such as pregnancy tests and
rapid drug test devices.
How sensitive are rapid drug
tests?
The limit of detection (LOD) of
rapid drug tests for drugs in urine is usually a few nanograms to a few hundred
nanograms per milliliter. This sensitivity is sufficient for detecting
most drugs of abuse in urine after drug use. The detection window of drugs in
urine is usually a few days after drug use. Drugs in saliva last shorter time
than in urine, normally one or two days.
How accurate are the results of
rapid tests?
The test results are generally
> 90% accurate in indicating diseases or health states, however, rapid tests are not totally reliable
for making diagnostic decisions. Other clinical findings must be considered when
a diagnosis is made. Rapid tests are in most
cases a prescreening test means only. Once a sample is tested positive,
a more reliable laboratory test method is recommended for confirmation of the
positive result. For example, a positive rapid drug test result is not
sufficient to prove one has used the drug. A confirmation test method, such as
GC/MS analysis of the urine sample is recommended before proving one is guilty.
The quality of rapid tests from different manufactures vary significantly.
How stable are rapid tests or
rapid drug tests?
Rapid tests contains dry reagents
only are usually table at room temperatures for about 18 months to 25 months.
Like most biological products, the degradation of rapid test reagents is
temperature sensitive. For longer term storage the products should be stored at
cool places and avoid extreme high temperature conditions and direct sunlight in storage
or during transportation. The relationship of shelf life and storage temperature
is best described by Arrhenius equation.
How are shelf lives of rapid test
devices determined?
The same question may be asked as
how are shelf lives or rapid drug tests or OTC pregnancy tests determined. There
are two ways to study biological material stability/shelf life. One is real time
study and the other is temperature accelerated stability study.
The Food and Drug Administration (FDA) requires product expiry dating based on
real time stability data only. More details.
Rapid Test References
About Drug Testing
Stability
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