From the Guidelines
A false positive strep test result is most likely due to the presence of non-pathogenic strep bacteria, cross-reactivity with other bacteria, or technical errors in test processing, occurring in about 5% of rapid strep tests, as most RADTs have an excellent specificity of 95% compared to blood agar plate culture 1. When considering the cause of a false positive strep test result, it's essential to understand the limitations of rapid antigen detection tests (RADTs) and throat cultures.
- The specificity of RADTs is high, ranging from 95% to 99%, which means that false-positive results are relatively rare 1.
- However, the sensitivity of RADTs can be lower, ranging from 80% to 90%, which may lead to false-negative results, particularly in patients who are carriers of group A streptococci 1.
- Technical errors in test processing, such as improper swabbing or handling of the specimen, can also contribute to false-positive results.
- The presence of non-pathogenic strep bacteria that normally live in the throat can also lead to false-positive results, as these bacteria may be detected by the RADT or throat culture.
- Cross-reactivity with other bacteria can also occur, leading to false-positive results. To minimize the risk of false-positive results, healthcare providers should consider both test results and clinical symptoms when making treatment decisions.
- If a patient receives a positive rapid strep test result but has minimal symptoms or other clinical factors suggesting they don't have strep throat, a backup throat culture may be ordered to confirm the diagnosis before prescribing antibiotics.
- This approach helps prevent unnecessary antibiotic use, which contributes to antibiotic resistance and exposes patients to potential side effects without benefit 1.
From the Research
Causes of False Positive Strep Test Results
- The provided studies do not directly address the causes of false positive strep test results 2, 3, 4, 5, 6.
- However, it can be inferred that false positive results may occur due to various factors such as:
- Poor quality of the specimen 2
- Incorrect interpretation of test results
- Contamination of the sample
- Limitations of the testing method itself
- The studies focus more on the diagnosis and treatment of streptococcal pharyngitis, and the importance of accurate testing and confirmation of results 4, 6.
- The use of rapid antigen tests and throat cultures is discussed, along with their respective advantages and limitations 2, 4, 6.
- It is essential to note that false positive results can have significant consequences, including unnecessary antibiotic treatment and potential contributions to antibiotic resistance.