Comparison of the Quantitative DiaSorin Liaison Antigen Test to Reverse Transcription-PCR for the Diagnosis of COVID-19 in Symptomatic and Asymptomatic Outpatients

We evaluated the quantitative DiaSorin Liaison severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen test in symptomatic and asymptomatic individuals consulting their general practitioners (GPs) during a period of stable intense virus circulation (213/100,000 habitants per day). Leftover reverse transcription-PCR (RT-PCR) positive (n= 204) and negative (n= 210) nasopharyngeal samples were randomly selected among fresh routine samples collected from patients consulting their GPs. Samples were tested on Liaison XL according to the manufacturer's instructions. Equivocal results were considered negative. The overall sensitivity and specificity of the Liaison antigen test compared to RTPCR were 65.7% (95% confidence interval [CI], 58.9% to 71.9%) and 100% (CI, 97.8% to 100%). Sensitivity in samples with viral loads of >10(5), >10(4), and >10(3) copies/ml were 100% (CI, 96.3% to 100.0%), 96.5% (CI, 91.8% to 98.7%), and 87.4% (CI, 81.3% to 91.5%), respectively. All samples with #103 copies/ml were antigen negative. The ratio of antigen concentration to viral load in samples with = 10(5) copies/ml) was not significantly higher in symptomatic than in asymptomatic participants (63.9% [CI, 54.9% to 72.0%] versus 51.9% [CI, 41.1% to 62.6%]; P = 0.11), but the proportion of participants with a low viral load (= 10(4) copies/ml were 96.5% and 100%. The correlation of antigen concentration with viral load was comparable in symptomatic and asymptomatic individuals.