When to Perform a Rapid Strep Test
Perform a rapid strep test immediately when a patient presents with clinical features suggesting Group A streptococcal pharyngitis, specifically when they have sudden onset sore throat combined with fever, tonsillar exudate, or tender anterior cervical lymphadenopathy—but avoid testing when obvious viral features like cough, coryza, or conjunctivitis are present. 1
Clinical Timing Algorithm
Immediate Testing Indicated When:
Acute presentation with streptococcal features: Test when patients present with sudden onset of sore throat, fever, headache, nausea, vomiting, or abdominal pain 1
Physical examination findings: Proceed with testing when you identify tonsillar exudate, cervical lymphadenitis, or pharyngeal erythema 2
Age 3-15 years with pharyngitis: This age group has the highest incidence and warrants testing when symptomatic 1, 2
Do NOT Test When:
Viral features dominate: Avoid testing if the patient has conjunctivitis, coryza, cough, diarrhea, hoarseness, discrete ulcerative stomatitis, or viral exanthem—these indicate viral etiology 1
Children under 3 years: Generally do not test this age group unless special risk factors exist (such as an older sibling with confirmed GAS infection), as incidence is low and rheumatic fever is rare 1
Asymptomatic contacts: Never test household contacts without symptoms 1
Age-Specific Testing Approach
Children and Adolescents (3-18 years):
- Perform RADT when clinical features suggest possible streptococcal pharyngitis 1
- Critical caveat: Always follow negative RADT with throat culture confirmation due to 80-90% sensitivity of rapid tests 3, 4
- The backup culture is essential because false-negative RADTs often occur in truly infected patients, not just carriers 3
Adults:
- Perform RADT when clinical features suggest possible streptococcal pharyngitis 1
- No backup culture needed after negative RADT in adults due to low incidence of streptococcal pharyngitis and minimal risk of rheumatic fever 1
Test Performance Characteristics That Guide Timing
High specificity (≥95%) means you can confidently treat based on a positive RADT result without culture confirmation 3, 4
Moderate sensitivity (80-90%) means negative results require culture backup in children, which adds 18-24 hours (and up to 48 hours for final reading) to the diagnostic timeline 3
The speed advantage of RADT (results in minutes) allows same-visit treatment decisions, reducing spread of infection and allowing faster return to school or work 3, 4
Common Pitfalls to Avoid
Don't test if you've already decided to treat empirically: If clinical criteria alone lead you to prescribe antibiotics covering streptococcus, testing is unnecessary—though this approach leads to antibiotic overuse 5, 1
Don't use antibody titers for acute diagnosis: Anti-streptococcal antibody tests reflect past infections, not current pharyngitis, and should never guide acute management 6, 1
Don't test too early after antibiotic exposure: False-negative results occur if the patient received antibiotics shortly before or at the time of specimen collection 3
Don't rely on colony count: The number of streptococcal colonies on culture plates cannot reliably distinguish true infection from carrier state 3
Special Circumstances for Testing
Recent streptococcal pharyngitis (within 28 days): RADT remains both sensitive and specific in this setting, contrary to concerns about antigen persistence causing false positives 7
Severe symptoms: When patients present with severe symptoms, rapid testing is particularly valuable for early detection and treatment initiation 5
Post-treatment follow-up: Do not routinely perform testing after treatment completion unless special circumstances exist 1