Nasopharyngeal Panbio COVID-19 antigen performed at point-of-care has a high sensitivity in symptomatic and asymptomatic patients with higher risk for transmission and older age

Masiá, Mar; Fernández-González, Marta; Sánchez, Manuel; Carvajal, Mar; García, José Alberto; Gonzalo, Nieves; Ortiz de la Tabla, Victoria; Agulló, Vanesa; Candela, Inmaculada; Guijarro, Jorge; Gutiérrez, José Antonio; de Gregorio, Carlos; Gutiérrez, Félix

BACKGROUND: Performance of point-of-care tests in different clinical scenarios and on different samples remains undetermined. We comprehensively evaluated the performance of the nasopharyngeal Panbio COVID-19 antigen Rapid-Test-Device. METHOD: Prospective study including consecutive patients attending three primary care centers (PCC) and an emergency department. The antigen test was performed at point-of-care in nasopharyngeal and nasal swabs, and in saliva. Positive and negative percent agreement (PPA, NPA) were calculated with the RT-PCR assay as reference standard. RESULTS: Of 913 patients included, 296 (32.3%) were asymptomatic and 690 (75.6%) came from the PCC. Nasopharyngeal swabs were collected from 913, nasal swabs from 659, and saliva from 611 patients. RT-PCR was positive in 196 (21.5%) nasopharyngeal samples (NPS). Overall PPA (95% CI) in NPS was 60.5% (53.3-67.4), and it was lower in nasal swabs (44.7%) and saliva (23.1%). Test performance in NPS was largely dependent on the cycle threshold (Ct) in RT-PCR, with PPA of 94% for Ct≤25 and 80% for Ct<30. In symptomatic patients, the PPA was 95% for Ct≤25; 85% for Ct<30, and 89% for the symptom triad of fever, cough and malaise. Performance was also dependent on age, with PPA of 100% in symptomatic patients >50 years with Ct<25. In asymptomatic patients, the PPA was 86% for Ct<25. In all cases, NPA was 100%. CONCLUSION: The nasopharyngeal Panbio COVID-19 antigen test performed at point-of-care has a good sensitivity in symptomatic patients with Ct<30 and older age. The test was useful to identify asymptomatic patients with lower Ct values.