What tests are used to diagnose the cause of a sore throat?

Diagnostic Tests for Sore Throat

For diagnosing the cause of a sore throat, clinical scoring systems combined with selective use of rapid antigen detection tests (RATs) should be used, with throat cultures reserved for specific situations. 1

Clinical Assessment

The first step in diagnosing sore throat is using a clinical scoring system:

Centor Score

• Assess for four criteria 1:
  1. Fever by history or temperature >38°C
  2. Tonsillar exudates
  3. Tender anterior cervical adenopathy
  4. Absence of cough

Modified Centor Score

• Adds age criteria to the standard Centor score 2:
  • Age 3-14 years: +1 point
  • Age 15-44 years: 0 points
  • Age ≥45 years: -1 point

Diagnostic Algorithm

1. Low probability of streptococcal infection (0-1 Centor criteria):

   • No further testing needed
   • No antibiotics recommended 1

2. Intermediate probability (2 Centor criteria):

   • Consider RAT if available
   • Manage based on test results 1

3. High probability (3-4 Centor criteria):

   • Perform RAT 1
   • If RAT positive: treat for Group A Streptococcus (GAS)
   • If RAT negative: no need for throat culture in adults 1

Laboratory Tests

Rapid Antigen Detection Tests (RATs)

• When to use: For patients with high likelihood of streptococcal infection (3-4 Centor criteria) 1
• Technique: Swab should be performed on both tonsils and posterior pharyngeal wall 1
• Interpretation:
  • Positive result: Treat for GAS
  • Negative result in adults: No further testing needed 1
  • Negative result in children: Some guidelines recommend confirmation with throat culture 1

Throat Culture

• Role: Not necessary for routine diagnosis of acute sore throat 1
• When to consider:
  • In research settings
  • When tracking antibiotic resistance
  • In areas with high prevalence of rheumatic fever
  • For suspected rare throat infections 1

Additional Tests

• C-reactive protein (CRP): Not helpful in diagnosing GAS pharyngitis 1
• Anti-DNase B: Not recommended for routine diagnosis (requires serial tests) 1
• Viral testing: May be considered in research settings but not routine practice 3

Special Considerations

Viral vs. Bacterial Differentiation

• Viral pharyngitis often presents with:
  • Cough
  • Rhinorrhea (runny nose)
  • Stuffy nose
  • Sneezing
  • Absence of tonsillar exudate 3

Warning Signs for Serious Conditions

• Evaluate for rare but serious throat infections if patient presents with 1:
  • Difficulty swallowing
  • Drooling
  • Neck tenderness or swelling
  • Severe symptoms

Pitfalls to Avoid

1. Overdiagnosis of bacterial pharyngitis: Most sore throats (>70%) are viral in origin 4, 3

2. Unnecessary antibiotic prescribing: Using clinical scoring and RATs can reduce inappropriate antibiotic use 1

3. Inadequate sampling technique: RAT accuracy depends on proper sampling from both tonsils and posterior pharyngeal wall 1

4. Ignoring age-related differences: The Centor score has lower utility in children due to different clinical presentations 1

5. Relying solely on clinical judgment: Clinical signs and symptoms alone have limited diagnostic accuracy (positive likelihood ratios range 1.45-2.33) 4

The diagnostic approach to sore throat should focus on identifying patients who truly need antibiotics while avoiding unnecessary testing and treatment in those with likely viral etiology. The combination of clinical scoring systems with selective use of RATs provides the most efficient and evidence-based approach to diagnosis.