Sensitivity, specificity and predictive values of molecular and serological tests for COVID-19. A longitudinal study in emergency room

Bisoffi, Zeno; POMARI, ELENA; Deiana, Michela; Piubelli, Chiara; Ronzoni, Niccolo; Beltrame, Anna; Bertoli, Giulia; Riccardi, Niccolo; Perandin, Francesca; Formenti, Fabio; Gobbi, Federico; Buonfrate, Dora; Silva, Ronaldo

Accuracy of diagnostic tests is essential for suspected cases of Coronavirus Disease 2019 (COVID-19). This study aimed to assess the sensitivity, specificity and positive and negative predictive value (PPV and NPV) of molecular and serological tests for the diagnosis of SARS-CoV-2 infection. A total of 346 consenting, adult patients were enrolled at the emergency room of IRCCS Sacro Cuore Don Calabria Hospital, Negrar, Italy. We evaluated three RT-PCR methods including six different gene targets; five serologic rapid diagnostic tests (RDT); one ELISA test. The final classification of infected/not infected patients was performed using Latent Class Analysis in combination with clinical re-assessment of incongruous cases and was the basis for the main analysis of accuracy. Of 346 patients consecutively enrolled, 85 (24.6%) were classified as infected. The molecular test with the highest sensitivity, specificity, PPV and NPV was RQ-SARS-nCoV-2 with 91.8% (C.I. 83.8-96.6), 100% (C.I. 98.6-100.0), 100.0% (C.I. 95.4-100.0) and 97.4% (C.I. 94.7-98.9) respectively, followed by CDC 2019-nCoV with 76.2% (C.I. 65.7-84.8), 99.6% (C.I. 97.9-100.0), 98.5% (C.I. 91.7-100.0) and 92.9% (C.I. 89.2-95.6) and by in-house test targeting E-RdRp with 61.2% (C.I. 50.0-71.6), 99.6% (C.I. 97.9-100.0), 98.1% (C.I. 89.9-100.0) and 88.7% (C.I. 84.6-92.1). The analyses on single gene targets found the highest sensitivity for S and RdRp of the RQ-SARS-nCoV-2 (both with sensitivity 94.1%, C.I. 86.8-98.1). The in-house RdRp had the lowest sensitivity (62.4%, C.I. 51.2-72.6). The specificity ranged from 99.2% (C.I. 97.3-99.9) for in-house RdRp and N2 to 95.0% (C.I. 91.6-97.3) for E. The PPV ranged from 97.1% (C.I. 89.8-99.6) of N2 to 85.4% (C.I. 76.3-92.00) of E, and the NPV from 98.1% (C.I. 95.5-99.4) of gene S to 89.0% (C.I. 84.8-92.4) of in-house RdRp. All serological tests had <50% sensitivity and low PPV and NPV. One RDT (VivaDiag IgM) had high specificity (98.5%, with PPV 84.0%), but poor sensitivity (24.7%). Molecular tests for SARS-CoV-2 infection showed excellent specificity, but significant differences in sensitivity. As expected, serological tests have limited utility in a clinical context.