Investigations
Your Organisational Guidance
ebpracticenet urges you to prioritise the following organisational guidance:
Acute KeelpijnPublished by: Werkgroep Ontwikkeling Richtlijnen Eerste Lijn (Worel)Last published: 2017Mal de gorge aiguPublished by: Groupe de Travail Développement de recommmandations de première ligneLast published: 20171st investigations to order
rapid antigen test for group A Streptococcus (GAS)
Test
Rapid antigen detection tests for GAS offer the advantage of immediate point-of-care testing and are about 70% to 90% sensitive and 95% specific compared with throat culture.[1][30][31]
GAS rapid antigen detection tests may have a lower specificity in children recently treated for GAS.[32]
When GAS is suspected, a negative antigen test should be followed up with throat culture, especially in children, given their increased risk of rheumatic fever.[4][33]
Positive testing in the absence of characteristic symptoms (fever, lack of cough, tonsillar exudates, and tender cervical adenopathy) likely represents colonisation and is not clinically relevant; therefore, testing should be used only when the clinical symptoms are consistent with GAS disease. Testing patients without the appropriate symptoms often leads to misdiagnosis and inappropriate use of antibiotics. Results are typically available in 10-20 minutes.
The UK National Institute for Health and Care Excellence recommends against using rapid antigen tests for GAS infections in people aged 5 and over with a sore throat on the grounds of clinical effectiveness in affecting outcomes and microbial stewardship, compared to clinical scoring systems alone.[34]
Result
positive in GAS infection and asymptomatic colonisation
nucleic acid amplification (via polymerase chain reaction) for group A Streptococcus (GAS)
Test
Comparable to throat culture in sensitivity and specificity but gives more rapid results (even in primary care); however, rapid in-office PCR is not widely available.
Result
positive in GAS infection
Investigations to consider
culture of throat swab for group A Streptococcus (GAS)
Test
A throat culture for GAS is the most sensitive (90% to 95%) and specific test for GAS.[1] It is considered the gold standard and may be helpful if the clinical suspicion of GAS is high or disease is caused by other streptococci or other bacterial pathogens such as Achanobacter hemolyticum.[4][25]
Culture is recommended in any child that is negative for GAS via rapid antigen detection testing but who has clinical signs and symptoms consistent with GAS pharyngitis.[4][33]
Throat culture is particularly useful when rapid antigen tests are negative for GAS but the clinical syndrome is consistent with GAS.[4] Rapid antigen tests will not detect other streptococci or Arcanobacterium haemolyticum that can be clinically indistinguishable from GAS pharyngitis.
Result
growth of GAS
culture or PCR of throat swab for gonococcus or chlamydia
Test
Pharyngeal swab for gonococcus or chlamydia should be considered when there is a history of sexual activity or suspicion of sexual abuse.
Result
positive growth on culture
serum monospot for Epstein-Barr virus infection
Test
The Centers for Disease Control and Prevention recommend that the Monospot test is not used. The antibodies detected by Monospot can be caused by conditions other than infectious mononucleosis and does not confirm the presence of EBV infection.[39]
Result
positive heterophile antibodies
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