Investigations

There are a number of strategies that can be employed in the investigation of patients with a sore throat:

Rapid streptococcal antigen testing

In the USA, and other countries without universal primary care backup, rapid streptococcal antigen testing has been widely utilised in the ED. The test is claimed to be 95% sensitive and specific but, in some studies, sensitivity has varied between 55% and 90% and has also been found to vary considerably depending on the operator performing the test [12].

In one study carried out in UK ED setting, rapid streptococcal antigen testing was found to have a sensitivity of 66% but 99% specificity [13]. Although included in NICE guidance, not all UK EDs have access to rapid streptococcal antigen testing.

Antistreptolysin O titre (ASOT)

A rising antistreptolysin O titre (ASOT) provides the gold standard criteria for immunologically significant GABHS infection. However, it is impractical and unnecessary in the vast majority of cases of sore throat.

Throat swab

Throat swabs, although widely used, are reliant on correct technique and interpretation is complicated by asymptomatic carriers of GABHS.

Covid-19 swab

It is recognised that sore throat can be a symptom of Covid-19. By itself it is not necessitate a PCR test, however clinicians should consider if there are other symptoms such as fever, new continuous cough or loss/change to sense or taste or smell [24]. 

Other investigations

Other investigations which may be useful in patients with a sore throat include:

• Routine bloods should be taken if the patient is being cannulated for another reason e.g. unable to swallow. These may show signs of dehydration
• FBC will likely show leucocytosis. A raised WBC count with lymphocytosis and atypical lymphocytes is suggestive of infectious mononucleosis
• Heterophile antibody tests for infectious mononucleosis e.g. Monospot and Paul Bunnell tests
• Deranged liver function tests are present in 90% of patients with Infectious Mononucleosis
• Chest x-ray if respiratory infection is suspected
• Fibreoptic Nasal Endoscopy (FNE) can be performed by ENT specialists in ED to visualise the pharynx and glottis. It is particularly of use in patients presenting with stridor
• Lateral soft tissue neck x-ray for retropharyngeal abscess and epiglottitis.

An epiglottic width (widest anteroposterior diameter of the epiglottis) of >7 mm was found to have a sensitivity and specificity of 100% for the diagnosis of epiglottitis in one study [14] (see image below).