Investigations
1st investigations to order
throat culture
Test
Testing for presence of bacteria is not absolutely necessary, although it is routinely performed in parts of the US (more than in most other parts of the world).
Throat culture is the standard test for the definitive diagnosis of bacterial tonsillitis; however, the delay in results (usually more than 48 hours) limits its usefulness as a first test.
If the culture is performed in Thayer-Martin medium, it can also grow Neisseria gonorrhoeae.[2]
Result
culture of pathogen
rapid streptococcal antigen test
Test
Sensitivity is lower than with culture but it has the benefit of providing immediate results.
This test should be ordered in children over 3 years old and adults with high probability of group A beta-haemolytic streptococci (GABHS) infection, as assessed by at least three Centor criteria. Due to its lower negative diagnostic value, a negative result may need to be confirmed with a negative throat culture or a nucleic acid amplification test in all ages.[2][15] Rapid testing may prevent against unnecessary use of antibiotics compared with standard care.[21]
Result
identification of GABHS
Investigations to consider
serological testing for streptococci
Test
May be useful in suspected rheumatic fever.
Antistreptolysin O (ASO), antideoxyribonuclease B, or other streptococcal antibody titres (e.g., hyaluronidase, streptokinase, or nicotinic acid dehydrogenase) are measured. However, diagnostic rises occur after 2 or 3 weeks, which limits their usefulness.
Result
considered positive if there is a fourfold rise in antibody titres
WBC count and differential
Test
Useful in patients with suspected infectious mononucleosis, in immunocompromised patients, and in patients with signs or symptoms of severe infection or sepsis.
A raised WBC count with neutrophilia is suggestive of a bacterial infection, whereas a raised WBC count with lymphocytosis and atypical lymphocytes is suggestive of infectious mononucleosis.
Result
may show raised neutrophil and/or lymphocyte count
heterophile antibodies
Test
Should be performed in patients with symptoms that persist and in those with posterior (as well as anterior) cervical lymphadenopathy.
False negatives in adults account for about 25% of results in the first week of symptoms but are subsequently lower. The sensitivity is even lower in children.[16]
Result
may show presence of heterophile antibodies as detected on Monospot or other rapid diagnostic tests
vaginal and cervical, or penile, and rectal cultures
Test
Should be performed in patients suspected of gonococcal pharyngitis, in particular those engaging in oral-genital sex.
Result
may show positive culture (Thayer-Martin medium) for Neisseria gonorrhoeae
HIV viral load assay
Test
Indicated in high-risk patients with persistent infection and severe constitutional symptoms (malaise, tiredness, weight loss, generalised lymphadenopathy).
Result
may show ≥10,000 HIV RNA copies/mL
lateral cervical view x-ray, exposed for soft tissue
Test
Should be performed in patients who do not improve, in those who present with severe symptoms and/or significant trismus (lockjaw), and in those with neck swelling.
Result
may show enlarged retropharyngeal and posterior oropharyngeal soft tissue
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