Does the rapid streptococcal (strep) antigen detection test have a high rate of false negatives?

From the Guidelines

Yes, rapid strep tests do have a significant rate of false negatives, with approximately 10-30% of negative results being incorrect, as the sensitivity of most rapid antigen detection tests (RADTs) is 70%–90% compared to blood agar plate culture 1. This means that while a positive result is highly reliable, a negative result doesn't definitively rule out strep throat. For this reason, healthcare providers often send a throat culture to confirm negative rapid test results, especially in children and adolescents where accurate diagnosis of strep throat is important to prevent complications like rheumatic fever. The false negatives occur because rapid tests detect bacterial antigens and require a substantial bacterial load to show positive, whereas cultures can detect smaller amounts of bacteria. Some key points to consider include:

• The specificity of RADTs is approximately 95%, making false-positive test results highly unusual 1.
• Newer tests based on enzyme immunoassay techniques offer increased sensitivity and a more sharply defined end point 1.
• The Clinical Laboratory Improvement Act of 1988 does not waive the need for certification for some RADTs, requiring proper certification of the physician’s laboratory 1.
• Factors that can increase false negatives include improper swabbing technique, testing too early in the infection, or prior antibiotic use.
• If strep throat is strongly suspected despite a negative rapid test, your doctor may either treat empirically or wait for culture results before making treatment decisions, typically with penicillin or amoxicillin for 10 days if strep is confirmed.
• According to the 2012 update by the Infectious Diseases Society of America, negative RADT tests should be backed up by a throat culture in children and adolescents, but not necessarily in adults 2.

From the Research

Rapid Strep Swab Accuracy

• The rapid strep swab has been shown to have a high specificity, with a study from 3 finding a specificity of 0.96, indicating a low rate of false positives.
• However, the sensitivity of the rapid strep swab has been found to be lower, with a meta-analysis from 4 estimating a sensitivity of 0.86, indicating a potential for false negatives.
• The study from 3 also found that the rapid strep test was more reliable in patients who had recent streptococcal pharyngitis, with a sensitivity of 0.91 compared to 0.70 in those without recent infection.
• Another study from 4 found that molecular-based rapid antigen diagnostic tests had the best diagnostic accuracy, with a sensitivity of 0.86 and a specificity of 0.96.

False Negative Rates

• The false negative rate of the rapid strep swab is a concern, as it may lead to undertreatment of streptococcal pharyngitis.
• A study from 5 recommends that a throat culture be performed after a negative rapid antigen test result in children and adolescents to confirm the diagnosis.
• The study from 4 found that the overall summary estimate for sensitivity of rapid antigen diagnostic tests was 0.86, indicating that approximately 14% of cases may be missed.
• The use of molecular-based rapid antigen diagnostic tests may help to reduce the false negative rate, as they have been shown to have higher sensitivity than other types of tests 4.