Sensitivity Rate of Strep Tests
The sensitivity of most Rapid Antigen Detection Tests (RADTs) for strep throat ranges between 80% and 90%, or even lower, when compared with blood agar plate culture. 1
Types of Strep Tests and Their Sensitivity
Rapid Antigen Detection Tests (RADTs)
- Sensitivity: 80-90% (or lower) compared to throat culture 1
- Specificity: ≥95% compared to throat culture 1
- Implications: High specificity means false-positive results are rare, allowing confident treatment decisions based on positive results
Different types of RADTs show varying sensitivity:
- First-generation tests (latex agglutination): Lower sensitivity, unclear endpoints 1
- Enzyme immunoassay (EIA) tests: Improved sensitivity, more defined endpoints 1
- Newer technologies (optical immunoassay, chemiluminescent DNA probes): Potentially higher sensitivity, approaching that of standard throat culture 1
Specific RADT Performance Examples
- careUS Strep A Plus: 92.5% sensitivity compared to culture 2
- SD Bioline: 71.6% sensitivity compared to culture 2
- BD Veritor: 74.6% sensitivity compared to culture 2
- QuickVue Dipstick Strep A test: 92% sensitivity in primary care settings 3
- DIAQUICK Strep A Blue Dipstick: 72% sensitivity in primary care settings 3
Clinical Implications of Test Sensitivity
Impact on Patient Management
- Due to the limited sensitivity of RADTs, a negative result should be confirmed with a conventional blood agar plate culture 1
- In a population of 1000 children with a 30% prevalence of Group A Streptococcus (GAS), approximately 43 patients with GAS will be missed by RADT alone 4
Factors Affecting Test Performance
- Patient selection: Sensitivity is higher (78%) in patients with higher clinical probability of strep throat (McIsaac score >2) 5
- Age groups: Sensitivity tends to be higher in children (70%) compared to adults (59.4%) 6
- Test technique: Proper specimen collection and healthcare worker training significantly impact test sensitivity 6
Best Practice Recommendations
- For positive RADT results: Treatment can be initiated immediately due to high specificity 1
- For negative RADT results: Confirm with throat culture before ruling out GAS pharyngitis 1
- Combined approach: Using RADT with backup culture for negative results increases sensitivity to approximately 85% 5
Common Pitfalls to Avoid
- Relying solely on negative RADT results: Due to limited sensitivity, this may lead to missed GAS cases
- Using RADTs without understanding their limitations: Different brands and technologies have varying sensitivity
- Misinterpreting test results in different populations: Test performance varies by age group and clinical presentation
- Confusing ASO titers with direct testing: ASO titers reflect past immunologic events and are not useful for diagnosing acute pharyngitis 1, 7
When selecting a strep test for clinical practice, consider both the sensitivity and specificity characteristics of the specific test being used, and implement appropriate follow-up protocols for negative RADT results.