Recommended Number of Drops for Strep A and B Rapid Antigen Detection Test
The specific number of drops for streptococcal A and B solution used in rapid antigen detection tests (RADTs) is not standardized across all test kits and should follow the manufacturer's instructions for each specific commercial kit. 1
General Information on RADTs for Strep Testing
- RADTs have been developed for the identification of group A β-hemolytic streptococci directly from throat swabs, providing faster results than conventional blood agar plate cultures 1
- These tests offer significant clinical advantages by allowing rapid identification and treatment of patients with streptococcal pharyngitis, which can reduce the risk of spread and decrease acute morbidity associated with the illness 1
- Most commercially available RADTs have excellent specificity (≥95%) compared with blood agar plate cultures, meaning false-positive results are rare 1
Test Procedure Considerations
The testing procedure typically involves:
The exact number of drops varies by manufacturer and test kit design, with each commercial kit providing specific instructions 3, 5
Test Performance Factors
- The sensitivity of most RADTs ranges between 80% and 90% when compared with blood agar plate culture 1
- Newer tests based on enzyme immunoassay (EIA) techniques, optical immunoassay (OIA), and chemiluminescent DNA probes may offer increased sensitivity 1
- Proper specimen collection and handling significantly impact test performance 2
- Following the manufacturer's instructions precisely, including the correct number of drops, is essential for optimal test performance 3
Common Pitfalls to Avoid
- Using incorrect volumes of reagents can lead to false results 2
- Not waiting the appropriate amount of time before reading results can affect accuracy 3
- Improper specimen collection (not swabbing both tonsils and posterior pharynx) may reduce sensitivity 1
- Failure to confirm negative RADT results with conventional blood agar plate culture may miss true infections, as a significant proportion of patients with false-negative RADT results are truly infected with group A β-hemolytic streptococci 1
Clinical Implications
- RADTs allow for immediate treatment decisions when positive, which can reduce complications and transmission 1
- The high specificity of RADTs means that positive results can be trusted and appropriate antibiotic therapy initiated without waiting for culture results 1
- For children and adolescents, negative RADT results should be confirmed with conventional throat culture due to the higher prevalence and clinical significance of GAS in this population 1