Liotti 2021.

Study characteristics
Patient Sampling	Unclear design estimating sensitivity and specificity; residual samples selected from 1 of 2 virology laboratories at 2 COVID‐19 reference hospitals: [1] RT‐PCR+ve for SARS‐CoV‐2 (n = 104) [2] RT‐PCR−ve for SARS‐CoV‐2 (n = 255) Recruitment: not stated Prospective or retrospective: retrospective
Patient characteristics and setting	Setting: unclear; laboratory samples Location: from study authors' institutions: Fondazione Policlinico Universitario A. Gemelli IRCCS, and Istituto Nazionale per le Malattie Infettive (INMI) Lazzaro Spallanzani IRCCS, Rome Country: Italy Dates: not stated Symptoms and severity: not stated Of SARS‐CoV‐2‐positive samples, 21, 20% high viral load (< 25 Ct), 83, 80% low viral load (≥ 25) [28, 27% with Ct ≥ 35) Demographics: not stated Exposure history: not stated
Index tests	Test name: STANDARD F COVID‐19 Ag FIA (no product codes reported) Manufacturer: SD Biosensor (Suwon, South Korea) Antibody: NP Ag target: monoclonal anti‐SARS‐CoV‐2 antibody Test method: FIA Samples used: NP; collection not reported Transport media: not stated Sample storage: performed within 24 h after collection on samples kept at 4 °C until testing Test operator: not stated; presume laboratory staff Definition of test positivity: as per manufacturer IFU Blinding reported: not stated Timing of samples: not reported
Target condition and reference standard(s)	Reference standard: RT‐PCR (1 of 4 assays); Altona Diagnostics RealStar SARS‐CoV‐2 RT‐PCR, the Seegene Allplex 2019‐nCoV, the DiaSorin SimplexaCOVID‐19 Direct or the Roche Diagnostics Cobas SARS‐CoV‐2 test Definition of non‐COVID cases: as for cases (single negative) Genetic target(s): not stated Samples used: NP (same as index) Timing of reference standard: not stated Blinded to index test: yes (performed first) Incorporated index test: no
Flow and timing	Time interval between index and reference tests: simultaneous (same swab) All participants received same reference standard: yes Missing data: none reported, no participant flow diagram reported Uninterpretable results: none reported Indeterminate results (index test): none reported FP results were re‐tested with Ag assay, 3 of 4 remained positive (all blood contaminated) Indeterminate results (reference standard): none reported Unit of analysis: not stated
Comparative
Notes	Funding: "study supported by funds to the Istituto Nazionale per le Malattie Infettive (INMI) Lazzaro Spallanzani IRCCS, Rome, Italy, from the Ministero della Salute (Ricerca Corrente, linea 1; COVID‐ 2020‐12371817), the European Commission e Horizon 2020 (EU project 101003544 e CoNVat; EU project 101003551 e EXSCALATE4CoV; EU project 12371675 e EXCALATE4CoV; EU project 101005075 e KRONO) and the European Virus Archive e GLOBAL (grants no. 653316 and no. 871029)." Publication status: published letter Source: Clinical Microbiology and Infection Author COI: all authors report no relevant conflicts of interest
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	Unclear
Did the study avoid inappropriate inclusions?	Unclear
Could the selection of patients have introduced bias?		Unclear risk
Are there concerns that the included patients and setting do not match the review question?			Unclear
DOMAIN 2: Index Test (Evaluations of single test application)
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
If a threshold was used, was it pre‐specified?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Unclear risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Unclear
DOMAIN 2: Index Test (Evaluations of serial (repeat) testing)
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	No
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
Reference standard does not incorporate result of index test?	Yes
Could the reference standard, its conduct, or its interpretation have introduced bias?		High risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			High
DOMAIN 4: Flow and Timing
Was there an appropriate interval between index test and reference standard?	Yes
Did all patients receive the same reference standard?	Yes
Were all patients included in the analysis?	Unclear
Did all participants receive a reference standard?	Yes
Could the patient flow have introduced bias?		Unclear risk