What is the next step if a rapid antigen test (RAT) for Group A Streptococcal infection is negative?

Management of Negative Rapid Antigen Testing for Group A Streptococcal Pharyngitis

When a rapid antigen detection test (RADT) for Group A Streptococcal pharyngitis is negative, a throat culture should be performed to confirm the negative result, particularly in children and adolescents.

Age-Based Approach to Negative RADTs

For Children and Adolescents:

• A negative RADT result should be confirmed with a conventional throat culture 1
• This recommendation is based on the limited sensitivity of RADTs (80-90% or lower) compared to throat culture 1, 2
• Many children with false-negative RADTs are truly infected with Group A streptococci and not merely carriers 1

For Adults:

• The Infectious Diseases Society of America (IDSA) guidelines indicate that confirmation of negative RADT results with throat culture may not be necessary in adults 1
• This is due to:
  • Lower incidence of streptococcal infection in adults
  • Extremely low risk of rheumatic fever in adults
  • High specificity of RADTs (≥95%) which minimizes over-prescription of antibiotics 1

Rationale for Confirmation Testing

The need for confirmation is based on several important factors:

• Test Sensitivity: Most RADTs have sensitivity between 80-90% when compared with blood agar plate culture 2
• Clinical Implications: Missing a Group A streptococcal infection can lead to:
  • Prolonged symptoms
  • Risk of suppurative complications
  • Potential for rheumatic fever (especially in children)
  • Continued transmission to close contacts 1
• Test Performance Variability: RADT performance varies based on:
  • The specific test being used
  • Proper specimen collection technique
  • Training of healthcare workers performing the test 2

Specimen Collection Considerations

To improve the accuracy of RADTs and subsequent throat cultures:

• Tests should be performed by trained staff 1
• Specimens should be collected from:
  • The posterior pharyngeal wall
  • Both tonsils 1
• Proper technique is essential as the quality of the specimen directly affects test results 3

Important Clinical Considerations

• If clinical suspicion for strep throat is high despite a negative RADT, consider:
  • Proceeding with throat culture
  • Evaluating the presence of clinical features (fever ≥38°C, lack of cough, tonsillar exudate, anterior cervical lymphadenopathy) 4
• The negative predictive value of RADTs is higher (up to 98%) when proper technique is used 4
• If antimicrobial therapy is initiated empirically while awaiting culture results, it should be discontinued if the culture is negative 1

Common Pitfalls to Avoid

1. Relying solely on clinical judgment: Clinical features alone are unreliable for diagnosis; the classic triad of fever, pharyngeal exudate, and tender anterior cervical adenopathy is present in only 15% of cases 5

2. Premature return to school/daycare: Children with confirmed Group A streptococcal pharyngitis should complete a full 24 hours of antibiotics before returning to school or daycare 6

3. Inappropriate use of antibiotics: Treating based on clinical suspicion alone without confirmation leads to overuse of antibiotics 7

4. Inadequate specimen collection: Poor sampling technique can lead to false-negative results in both RADTs and cultures 3

By following these evidence-based recommendations, clinicians can ensure appropriate diagnosis and management of Group A streptococcal pharyngitis, reducing both unnecessary antibiotic use and the risk of complications from untreated infections.