What laboratory tests should be ordered for a patient presenting with pharyngitis (sore throat)?

Laboratory Tests for Pharyngitis (Sore Throat)

For patients presenting with pharyngitis, laboratory testing should be guided by clinical features using the Centor criteria, with rapid antigen detection tests (RADTs) recommended for those with scores of 2-4, and throat cultures as backup for negative RADTs in children but not adults. 1, 2

Clinical Assessment to Guide Testing

• Testing for Group A Streptococcal (GAS) pharyngitis should be performed selectively based on clinical features, not routinely for all sore throats 2
• The Centor criteria should be used to determine which patients need testing: fever, tonsillar exudates, tender anterior cervical adenopathy, and absence of cough 3
• Testing is not recommended for patients with clinical features strongly suggesting viral etiology (cough, rhinorrhea, hoarseness, oral ulcers) 1
• Testing is not indicated for children under 3 years old due to low incidence of GAS and rare occurrence of rheumatic fever in this age group 1, 2

Recommended Laboratory Tests

• Rapid antigen detection test (RADT) is the first-line diagnostic test for patients with 2 or more Centor criteria 1, 3
• Throat culture remains the diagnostic standard with higher sensitivity than RADTs 4
• For children and adolescents, a negative RADT should be confirmed with a throat culture due to higher risk of complications 1, 5
• For adults, confirmation of a negative RADT with throat culture is generally not necessary due to lower incidence of GAS and minimal risk of rheumatic fever 1, 5

Biomarkers and Additional Testing

• Routine use of biomarkers such as C-reactive protein (CRP) or procalcitonin is not recommended for assessment of acute sore throat 1
• Anti-streptococcal antibody titers (e.g., ASO, anti-DNase B) are not recommended for routine diagnosis of acute pharyngitis 1, 5
• Erythrocyte sedimentation rate and CRP might be indicated only for suspected post-streptococcal complications, not routine diagnosis 1

Testing Algorithm Based on Age and Clinical Features

• For children ≥3 years and adolescents:

  • Score 0-1 Centor criteria: No testing needed 3
  • Score 2-4 Centor criteria: Perform RADT, if negative, confirm with throat culture 1, 3

• For adults:

  • Score 0-1 Centor criteria: No testing needed 3
  • Score 2-4 Centor criteria: Perform RADT only, no backup culture needed for negative results 1, 5

Common Pitfalls to Avoid

• Treating based on clinical symptoms alone without laboratory confirmation leads to antibiotic overuse 5, 2
• Testing patients with clear viral symptoms unnecessarily increases healthcare costs 2
• Improper swabbing technique can reduce test accuracy; proper technique requires swabbing both the posterior pharyngeal wall and tonsils 5
• Switching antibiotics without microbiological indication increases risk of adverse effects without clinical benefit 5

Laboratory testing for pharyngitis should be targeted and evidence-based to improve antibiotic stewardship, as studies show that using RADTs can significantly reduce unnecessary antibiotic prescriptions compared to empiric treatment 6, 7.