Will taking a dose of Augmentin (amoxicillin-clavulanate) affect the accuracy of a rapid strep test?

Will Augmentin Affect Rapid Strep Test Accuracy?

No, taking a single dose of Augmentin (or any antibiotic) before a rapid strep test will not make the test falsely negative, though antibiotics given shortly before or at the time of specimen collection can potentially cause false-negative results. 1

Understanding the Timing Issue

The concern about antibiotics affecting rapid strep test accuracy is valid but requires specific context:

• False-negative results can occur if the patient received antibiotics shortly before or at the time of specimen collection 1
• However, a single dose of Augmentin taken just before testing is unlikely to have eliminated enough bacterial antigen to cause a false-negative result, as the rapid antigen detection test (RADT) detects bacterial antigens present in the throat, not viable bacteria 1
• The RADT maintains excellent specificity (≥95%), meaning false-positive results are highly unusual 1
• The sensitivity of RADT ranges from 70-90% compared to throat culture, but this limitation exists regardless of recent antibiotic use 1

Clinical Decision Algorithm

If the patient has already taken one dose of Augmentin:

• Proceed with the rapid strep test - the single dose is unlikely to significantly affect results 1
• If the RADT is positive, treat confidently based on this result (specificity ≥95%) 1
• If the RADT is negative in a child or adolescent, obtain a backup throat culture due to the inherent 10-30% false-negative rate of RADT 1
• If the RADT is negative in an adult, no further testing is generally needed unless clinical suspicion remains very high 1

Important Caveats

The main concern is not the single dose itself, but rather:

• If the patient has been on antibiotics for 24 hours or more, bacterial counts may be significantly reduced, increasing the risk of false-negative results 1
• Proper swabbing technique is far more critical to test accuracy than timing - specimens must be obtained from both tonsillar surfaces and the posterior pharyngeal wall 1
• Research has shown that in patients with recent streptococcal pharyngitis, the rapid strep test actually appears more reliable (91% vs 70%) than in those without recent infection, suggesting antigen persistence does not cause false-positives 2

Bottom Line for Clinical Practice

Do not delay testing because of a single dose of Augmentin - proceed with the RADT and interpret results using standard algorithms based on patient age and clinical probability (Centor criteria). 1 The test's inherent sensitivity limitations are a greater concern than the single antibiotic dose, which is why backup cultures remain important in children regardless of antibiotic exposure. 1