From the Guidelines
The false negative rate for rapid streptococcal antigen detection tests using throat swabs is approximately 10-30%, as the sensitivity of most of these tests is 70-90% compared to blood agar plate culture. This means that 10-30% of patients who actually have strep throat will receive a negative result on the rapid test. Due to this significant false negative rate, clinical guidelines recommend that negative rapid strep test results should be confirmed with a throat culture, especially in children and adolescents 1. Throat cultures are considered the gold standard with higher sensitivity, though they take 24-48 hours for results. The false negative rate occurs because rapid tests require a substantial bacterial load to trigger a positive result, so early infections or those with lower bacterial counts may be missed. Factors that can increase false negatives include improper specimen collection technique, recent antibiotic use, or testing very early in the illness. Healthcare providers should consider clinical presentation alongside test results, particularly when symptoms strongly suggest strep throat despite a negative rapid test.
Some key points to consider when interpreting rapid strep test results include:
- The specificity of most rapid strep tests is approximately 95%, making false-positive test results highly unusual 1
- The sensitivity of rapid strep tests can vary depending on the population being tested, with lower sensitivity in children and adolescents 1
- Throat cultures may be affected by spectrum bias, which can impact the sensitivity of the test 1
- Clinical guidelines recommend confirming negative rapid strep test results with a throat culture, especially in children and adolescents 1
It is essential to note that the evidence from the 2012 study 1 is more recent and of higher quality compared to the 1997 study 1, and therefore, its findings should be prioritized when making clinical decisions. The use of rapid strep tests should be guided by clinical judgment and consideration of the potential for false negative results, and healthcare providers should be aware of the limitations of these tests when interpreting results and making treatment decisions.
From the Research
False Negative Rate for Rapid Strep Antigen Detection Tests
- The false negative rate for rapid streptococcal (strep) antigen detection tests using throat swabs can be determined by analyzing the sensitivity of the tests, as reported in various studies 2, 3, 4.
- According to a study published in 2017, the sensitivity of the Mascia Brunelli rapid antigen test was found to be 75.2% 2.
- Another study published in 2020 reported a sensitivity of 94.1% for the BD Veritor ™ System rapid antigen assay 3.
- A study from 2001 found that 2.4% of negative rapid antigen detection tests were actually throat culture positive, indicating a false negative rate of 2.4% 4.
- The false negative rate may vary depending on the specific test used and the population being tested, as seen in the differences in sensitivity reported by the studies 2, 3.
Factors Affecting False Negative Rate
- The density of GAS growth in the culture can affect the sensitivity of the rapid antigen test, as noted in the 2017 study 2.
- The age of the patient may also impact the false negative rate, with one study finding a higher rate of GAS positivity in the 5-15 age group 3.
- The use of different rapid antigen tests can result in varying false negative rates, as seen in the comparison of the Mascia Brunelli test and the QuickVue + Strep A Test 2.
Clinical Implications
- The false negative rate of rapid strep antigen detection tests has important implications for clinical practice, as it may lead to unnecessary antibiotic use or delayed treatment 2, 3.
- The studies suggest that confirmation of negative rapid antigen test results by culture may be necessary to prevent false diagnosis and incomplete treatment 2, 3, 4.