Bacterial Pharyngitis Workup

Updated: Feb 08, 2019
  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Approach Considerations

The probability that beta-hemolytic streptococci is causing the tonsillopharyngitis can be estimated using a diagnostic scoring system. [46]

The Centor score is a tool that was developed to help distinguish GAS pharyngitis from viral pharyngitis, so that antibiotics can be appropriately prescribed. It is calculated by assigning one point for each of the following: [46, 47]

  • Fever
  • Absence of cough
  • Presence of tonsillar exudates
  • Swollen, tender anterior cervical nodes

The Centor score can range from 0 to 4. [46, 47]

The McIsaac score modifies the Centor score by taking into account the differences in incidence of GAS infection in children versus older adults. The Centor score is used, but one point is added if the patient is younger than 15 years, while one point is subtracted if the patient is aged 45 years or older. [46, 47]

A score of 2 or more should prompt the clinician to perform a pharyngeal swab for rapid testing or bacterial culture to evaluate for beta-hemolytic streptococci. If the score is 3 or more, it would be reasonable for the clinician to treat as GAS pharyngitis. Routine blood tests for acute tonsillopharyngitis are unnecessary. Antistreptolysin O (ASO) testing and other antistreptococcal antibody testing provide no additional help in acute tonsillopharyngitis and so should not be performed. [46, 47]

The Centers for Disease Control and Prevention (CDC) and the American College of Physicians-American Society of Internal Medicine (ACP-ASIM) endorse the Centor score to determine the risk of GAS infection and to guide the management of acute pharyngitis in adults, as shown in Table 1. [47]

Table 1. CDC/ACP Acute Pharyngitis GAS Testing and Treatment Recommendations Based on Centor Score [47] (Open Table in a new window)

Centor score



Do not test. Do not treat.


Do not test. Do not treat.


Treat if rapid test result is positive for GAS.


Option 1: Treat if rapid test result is positive for GAS.


Option 2: Treat empirically.


Treat empirically.

The American Academy of Family Physicians also recommend the Centor score, as well as the FeverPAIN score as another validated clinical decision tool. The FeverPAIN scale for pharyngitis is discussed in Table 2. [48]

Table 2. FeverPAIN Scale for Pharyngitis [48] (Open Table in a new window)



Fever within the past 24 hours


Markedly inflamed tonsils


No coryza or cough


Presented within 3 days symptom onset


Purulence of tonsils


For a score of 0 or 1, no testing or treatment is recommended, although a backup throat bacterial culture can be considered if the patient is aged 3-15 years.

For a score of 2 or 3, a rapid antigen detection test is recommended.

For a score of 4 or 5, empiric antibiotic therapy is recommended.


Laboratory Studies

The clinical features of GABHS pharyngitis overlap significantly with that caused by non-GABHS. Microbiological testing provides data to help determine who may benefit from GABHS-directed therapy. Laboratory evaluation of pharyngitis falls into two broad categories: rapid antigen detection tests (RADT) and throat culture. [49] A throat culture is demonstrated in the video below.

Throat swab. Video courtesy of Therese Canares, MD; Marleny Franco, MD; and Jonathan Valente, MD (Rhode Island Hospital, Brown University).

RADTs offer the advantage of a speedy diagnosis, allowing for the proper administration, as well as proper withholding, of antibiotics. Drawbacks of RADTs include a higher cost and lower sensitivity compared with culture. While throat culture remains the gold standard for diagnosis of GABHS pharyngitis, it has a 24-48 hour turnaround time and entails more technical involvement. Both RADTs and throat culture cannot be used to differentiate between infection and colonization and, in some cases, may influence a physician to overuse antibiotics. For example, a child with coronavirus pharyngitis and GABHS colonization may be prescribed antibiotics based on a false–positive RADT result. No matter what type of test is used in the outpatient setting, judicious selection of patients to be screened is imperative in order to avoid a large number of false-positive results. [50]

Samples for RADT or throat culture should be obtained from the posterior pharynx or tonsils. Samples from the oral cavity result in a greatly reduced sensitivity.

Test of cure is not usually indicated except in special situations, [1] including the following:

  • Patients with a history of rheumatic fever
  • Patients who live in a community with an increased incidence of rheumatic fever or poststreptococcal glomerulonephritis
  • Patients involved in outbreaks of GABHS pharyngitis in closed or semiclosed communities

Test of cure should also be considered in members of a family in whom "ping-pong" spread is presumed.

Antistreptococcal antibody tests have no role in the diagnosis of acute bacterial pharyngitis. However, they may be used to confirm a history of exposure to GABHS in patients with suspected poststreptococcal glomerulonephritis or acute rheumatic fever.

Rapid antigen detection tests   [51]

See the image below.

Rapid antigen detection test for group A beta-hemo Rapid antigen detection test for group A beta-hemolytic streptococci.

All RADTs yield high specificity, allowing for prompt treatment of GABHS pharyngitis without the concern of false-positive results.

Initial RADTs relied on latex agglutination to identify cell wall carbohydrates obtained after acid extraction, a method associated with low sensitivity.

Newer RADTs use optical immunoassay (OIA) technology to identify cell wall carbohydrates. These yield a sensitivity that may be similar to that of throat culture. Nevertheless, before removing confirmatory throat cultures from any given clinical practice, verification of increased sensitivity is recommended.

A newer generation of rapid tests uses nucleic acid identification to identify GABHS-specific sequences. Such assays yield a specificity of 95%-100% and sensitivity in the range of 86%-95%. Although these tests provide an answer in hours, they rely on equipment not available in most outpatient settings and often need to be performed at a location other than the office.

Recent evidence showed that, without RADT, antibacterials are prescribed inappropriately in 41.6% of cases. RADT decreases this number to 11%. [52]

Throat culture

Considered the criterion standard of GABHS pharyngitis diagnosis, throat culture involves obtaining a sample from the posterior pharynx and tonsils and plating on sheep blood agar.

Bacitracin disks aid in differentiation of GABHS from other beta-hemolytic streptococci. A large zone of inhibition is found around GABHS but not around non–beta-hemolytic streptococci.

Cell wall carbohydrate detection assays, applied directly to the cultured bacteria, may also differentiate GABHS from other streptococci.


Imaging Studies

Imaging studies have no role in the diagnosis of bacterial pharyngitis. Lateral neck films may help to confirm the diagnosis of acute epiglottitis. CT scanning may aid in the diagnosis of some of the suppurative complications of pharyngitis, including retropharyngeal or deep neck abscesses, lymphadenitis, and sinusitis.