How Accurate is Lateral Flow Rapid Testing for SARS-CoV-2?
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
Prospective Cohort Study
20 independent general practitioners in Austria
Between October 22 and November 30, 2020
Patients with mild to moderate flu-like symptoms
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
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
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
Pre-test symptom duration: (P=0.0043)
Ct-value was positively correlated with pre-test symptom duration (P<0.001)
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
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