Performance of a SARS-CoV-2 antigen rapid immunoassay in patients admitted to the emergency department

• Published in: International journal of infectious diseases 2021-09, Vol.110, p.135-140
• Main Authors: Leli, Christian, Di Matteo, Luigi, Gotta, Franca, Cornaglia, Elisa, Vay, Daria, Megna, Iacopo, Pensato, Rosalia Emanuela, Boverio, Riccardo, Rocchetti, Andrea
• Format: Article
• Language: English
• Subjects: Aged; COVID-19; Diagnostic techniques and procedures; Emergency department; Emergency Service, Hospital; Hospitalization; Humans; Immunoassay; Microfluidic analytical techniques; Reverse transcriptase polymerase chain reaction; SARS-CoV-2; Sensitivity and Specificity
• ISSN: 1201-9712; 1878-3511
• DOI: 10.1016/j.ijid.2021.07.043

•RT-PCR is the gold standard for SARS-CoV-2 detection, but the results take time to appear•Rapid antigen tests are spreading, with extreme variability in diagnostic accuracy•The microfluidic antigen test showed excellent performance compared with the molecular one•A combination of the two tests improved the overall diagnostic capability Given the ongoing pandemic emergency, there is a need to identify SARS CoV-2 infection in various community settings. Rapid antigen testing is spreading worldwide, but diagnostic accuracy is extremely variable. Our study compared a microfluidic rapid antigen test with a reference molecular assay in patients admitted to the emergency department (ED) of a general hospital from October 2020 to January 2021. Nasopharyngeal swabs collected in patients with suspected COVID-19 and in patients with no symptoms suggesting COVID-19, but requiring hospitalization, were obtained. 792 patients of median age 71 years were included. With a prevalence of 21%, the results showed: 68.7% (95% confidence interval [CI]: 60.9–75.5) sensitivity; 95.2% (95% CI: 93.1–96.7) specificity; 79.2% (95% CI: 71.4–85.3) positive predictive value (PPV); 91.9% (95% CI: 89.5–93.9) negative predictive value; 3.8 (95% CI: 2.7–5.3) positive likelihood ratio (LR+); and 0.09 (95% CI: 0.07–0.1) negative likelihood ratio (LR−). In the symptomatic subgroup, sensitivity increased to 81% (95% CI: 70.3–88.6) and PPV to 96.9% (95% CI: 88.5–99.5), along with an LR+ of 32 (95% CI: 8.2–125.4). The new rapid antigen test showed an overall excellent diagnostic performance in a challenging situation, such as that of an ED during the COVID-19 emergency.