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* Pharyngitis
 #852904  
  lauram - 07/11/18 09:42
 
  A 3-year-old boy is brought to the clinic by his
mother. She is concerned because the patient
has complained of a sore throat over the past 4
days. He is not in day care and has had no
known sick contacts. His 7-year-old sister is
currently healthy. The physician does a throat
swab for a rapid streptococcal test and sends a second specimen for culture. Why does the
physician perform both tests?
(A) The culture may grow strains of bacteria
which are not detected by the rapid test
(B) The rapid streptococcal test and culture
both have high sensitivity
(C) The rapid streptococcal test and culture
both have high specificity
(D) The rapid streptococcal test has a high sensitivity, while the culture has high speci-
ficity
(E) The rapid streptococcal test has a high
specificity, while the culture has high sensitivity
 
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* Re:Pharyngitis
#3369310
  mobael - 07/14/18 14:37
 
  Answer is E
The specificity of RSTs(Rapid Strep test) for the presence of GAS(Group A Strept) is at least 95%, Therefore, if the test result is positive, the presence of GAS is highly likely. However, 5% to 20% of individuals carry GAS in their throats without symptomatic infection, so the presence of GAS in an individual with pharyngitis does not prove that this organism is responsible for the infection. The sensitivity of lateral flow RSTs is somewhat lower at 65% to 80%. Therefore, a negative result from such a test cannot be used to rule out GAS pharyngitis, a considerable disadvantage compared with microbial culture, which has a sensitivity of 90% to 95% this is why both are used.
 
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