False-Positive Rate of Rapid Strep Tests
Rapid antigen detection tests (RADTs) for group A streptococcal pharyngitis have an excellent specificity of ≥95%, meaning the false-positive rate is ≤5% and typically much lower. 1
Test Performance Characteristics
The high specificity of RADTs means that false-positive results are unusual, and therapeutic decisions can be made with confidence based on a positive test result. 1 This is the most clinically important characteristic of these tests from a treatment standpoint.
Key Performance Metrics
Specificity: ≥95% when compared with blood agar plate cultures, which translates to a false-positive rate of ≤5% 1
Sensitivity: 80-90% (or even lower in some populations), meaning false-negative results are the primary concern with RADTs, not false-positives 1
Recent research using polymerase chain reaction (PCR) testing suggests that the true specificity of RADTs may be even closer to 100%, as most apparent "false-positives" (76%) were actually associated with PCR-positive GAS results 2
Clinical Implications
Because false-positive results are rare, you can confidently initiate antibiotic therapy based on a positive RADT result without requiring confirmatory throat culture. 1 This stands in stark contrast to negative results, which require culture confirmation in children and adolescents.
The Real Problem: False-Negatives, Not False-Positives
The sensitivity limitations (80-90%) mean that 10-20% of true infections will be missed by RADTs, making false-negative results the clinically significant issue 1
Negative RADT results in children and adolescents (ages 3-18) must be confirmed with conventional blood agar plate culture due to this sensitivity limitation and the higher risk of rheumatic fever in this population 1
In adults, negative RADT results generally do not require culture confirmation because the prevalence of streptococcal pharyngitis and risk of rheumatic fever are both lower 1
Factors That Can Affect Test Accuracy
What Actually Causes Apparent False-Positives
Research suggests that many apparent false-positives on RADT (when culture is negative) may actually represent true GAS infections where bacterial inhibition by other organisms (such as Staphylococcus aureus) prevented culture growth 2
61% of culture-negative but RADT-positive cases were positive on both GAS PCR and S. aureus testing, suggesting bacterial interference rather than true false-positives 2
What Does NOT Increase False-Positives
Recent streptococcal pharyngitis does NOT increase the false-positive rate of RADTs, contrary to some clinical beliefs about antigen persistence 3
A study of 443 patients with recent streptococcal pharyngitis showed no difference in specificity (0.96 vs 0.98) compared to controls without recent infection 3
Common Pitfalls to Avoid
Do not order confirmatory cultures for positive RADT results – the high specificity makes this unnecessary and wastes resources 1
Do not dismiss a positive RADT as a "false-positive" in a patient with recent streptococcal pharyngitis – the specificity remains excellent in this setting 3
Do not confuse the false-positive rate (≤5%) with the false-negative rate (10-20%) – these are fundamentally different problems requiring different clinical approaches 1
Do not rely solely on negative RADTs in children without culture confirmation – the sensitivity limitations make this the critical testing gap, not false-positives 1