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COVID-19 Testing

How Accurate is Lateral Flow Rapid Testing for SARS-CoV-2?

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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

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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?

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