BACKGROUND AND PURPOSE:

• SARS-CoV-2 antigen detection via lateral flow testing (LFT) is faster than RT-PCR and useful for population-wide testing
• If rapid tests are accurate, patients could be managed based upon same-day test results
• Leber et al. (EClinicalMedicine, 2021) assessed the diagnostic accuracy of LFT compared to RT-PCR for SARS-CoV-2 detection

METHODS:

• Prospective Cohort Study
  • 20 independent general practitioners in Austria
  • Between October 22 and November 30, 2020
• Population
  • Patients with mild to moderate flu-like symptoms
• Exposures
  • Group 1 (true reactive): Suspected cases with reactive LFT and positive RT-PCR
  • Group 2 (false non-reactive): Suspected cases with a non-reactive LFT but positive RT-PCR
• Study design
  • All suspected COVID-19 cases received LFT and RT-PCR testing
  • Correlations were calculated, in including Cycle threshold (Ct)
  • Ct is a numerical value generated during a RT-PCR test that refers to the number of cycles needed for a sample to amplify and cross a threshold (cut-off) to be considered detected/positive | Ct values below the cutoff would be considered a true positive

RESULTS:

• 2562 symptomatic patients
  • Suspected COVID-19: 1037 patients
    • RT-PCR positives: 79.7%
• Among RT-PCR positives: 95.4% were LFT reactive (group 1)
  • Overall sensitivity: 95.4% (95% CI, 94 to 96.8)
  • Specificity: 89.1% (95% CI, 86.3 to 91.9)
  • Positive predictive value: 97.3% (95% CI, 95.9 to 98.7)
  • Negative predictive value: 82.5% (95% CI, 79.8 to 85.2)
• Reactive LFT and positive RT-PCR were positively correlated
• Reactive LFT was negatively correlated with
  • Ct-value (P<0.001)
  • Pre-test symptom duration: (P=0.0043)
• Ct-value was positively correlated with pre-test symptom duration (P<0.001)

CONCLUSION:

• Lateral flow rapid testing is an accurate method for diagnosing SARS-CoV-2 infection, with a sensitivity of 95.4% and specificity of 89.1%
• The authors conclude that the results of this study indicate that

…symptomatic antigen testing for SARS-CoV-2 with LFT delivered at scale in a general clinical setting such as primary care as early as onset symptom, and when viral load is high and Ct-value is low, can rapidly and accurately detect early COVID-19 among patients presenting with flu-like illness

Learn More – Primary Sources:

Comparing the diagnostic accuracy of point-of-care lateral flow antigen testing for SARS-CoV-2 with RT-PCR in primary care (REAP-2)

Tennessee Department of Health: Information on Cycle threshold (Ct) values for SARS-CoV-2

Related ObG Topics:

Saliva vs Nasopharyngeal Swabs for COVID-19 Testing: Do the Costs and Sensitivities Differ?

How Does the Rapid Antigen Test Perform Compared to PCR for Detecting SARS-CoV-2?

Can COVID-19 Be Detected Using a Breath Test?

What is the Probability of a False Negative When Taking a SARS-CoV-2 Test?