Rapid Strep Test (cont.)
Why is the rapid test better?
By comparison with culture methods, a rapid strep test is much quicker and
can produce results within minutes.
How is a rapid strep test done?
Obtaining a specimen is the same whether your doctor will do a throat culture
or rapid test for strep. A cotton swab (similar to a Q-tip) is quickly rubbed
over both tonsils as well as the back wall of the mouth (the posterior pharynx).
It is important to avoid contact with other structures inside the mouth such as
the tongue or cheeks. The
swab is then placed in a specialized container and the rapid test performed.
Many people find that obtaining the swab produces a gagging sensation. However, since the entire swabbing process lasts less than
five seconds this inconvenience is minimal.
What are the limitations of the rapid strep test?
There are several manufactures of rapid strep tests. All are designed to
respond only to the presence of the particular streptococcal bacteria (Group A)
responsible for strep throat. Other bacteria which are less much less likely to
cause pharyngitis are not identified by the rapid strep test.
- The test will not
detect viral causes of pharyngitis.
- A positive test response occurs when a
reaction between a protein on the surface of strep bacteria and chemicals in the
test materials exists. Either living or dead strep bacteria will produce a
positive reaction.
- Most rapid strep tests have a
sensitivity of 95%, meaning that
the test will be positive in 95 of 100 patients who are documented to have strep
throat via throat culture obtained at the same time. Since 5 of 100 patients
with strep throat will be missed using a rapid strep test, all negative swab
specimens should be sent for culture to confirm the absence of strep bacteria.
- A
positive culture requires antibiotics.
- The rapid strep test has a 98%
specificity. This
means that 98 of 100 positive tests correctly indicate the
presence specifically of Group A streptococcus bacteria; 2 of 100 positive
results are "false positives" - indicative of similarities between various surface
proteins found on strep bacteria and other non-strep bacteria found in the
mouth.
Last Editorial Review: 1/27/2009
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