Imai 2020.

Study characteristics
Patient Sampling	Purpose: Diagnosis of acute‐phase COVID‐19 Design: Two‐group study estimating sensitivity and specificity: [1] Patients with laboratory‐confirmed COVID‐19, including 74 symptomatic and 38 asymptomatic (total n = 112) [2] Pre‐pandemic samples from patients at Saitama Medical University Hospital (n = 48) Recruitment: Not reported Prospective or retrospective: Not reported Sample size: 160 (112) Further detail: NO further details
Patient characteristics and setting	Setting: Hospital inpatients Location: Self‐Defense Forces Central Hospital and Saitama Medical University Hospital Country: Japan Dates: [1] February 11 to March 31, 2020 Symptoms and severity: 74, 66% symptomatic (fever, cough, nasal discharge, diarrhoea, malaise, dyspnoea, tachypnoea, peripheral capillary oxygen saturation < 93%, and need for oxygen therapy) Demographics: Median age (IQR) 67 y (45–74 y); 64 (57.1%) male Exposure history: Not reported Non‐Covid group 1: Pre‐pandemic samples Source: Saitama Medical University Hospital; April to October 2019 Characteristics: not stated
Index tests	Test name: One Step Novel Coronavirus (COVID‐19) IgM/IgG Antibody Test Manufacturer: Artron, Burnaby, Canada Antibody: IgM, IgG Antigen target: not stated Evaluation setting: POC; evaluation setting not reported (appeared to be lab‐based) Test method: LFA Timing of samples: day of admission and during hospitalisation (within 1 week (n = 90), 1–2 weeks (n = 25), and > 2 weeks after onset (n = 24) Samples used: serum Test operator: Not stated Definition of test positivity: the presence of both the control line and the IgM or IgG antibody line indicated a positive result for IgM or IgG antibody, respectively. Blinding reported: no Threshold predefined: Yes, according to manufacturer’s instructions.
Target condition and reference standard(s)	Reference standard: RT‐qPCR for SARS‐CoV2 Samples used: pharyngeal and nasopharyngeal swabs Timing of reference standard: [1] Of the 74 symptomatic patients, median time from onset to admission was 5 days (IQR, 2–7 days); [2] Of the 38 asymptomatic patients, median time from the first RT‐qPCR–positive day to admission was 5 days (IQR, 3–6 days). Blinded to index test: Yes Incorporated index test: no Definition of non‐COVID cases: Pre‐pandemic Samples used: serum Timing of reference standard: NA Blinded to index test: yes Incorporated index test: no
Flow and timing	Time interval between index and reference tests: unclear All patients received same reference standard: yes Missing data: None reported Uninterpretable results: None reported Indeterminate results: None reported Unit of analysis: Samples; reported in two time periods
Comparative
Notes	Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or nonprofit sectors Publication status: Published Source: Journal of Clinical Virology Author COI: The authors declared that they had no conflicts of interests.
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?	No
Did the study avoid inappropriate exclusions?	Unclear
Did the study avoid inappropriate inclusions?	Unclear
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			High
DOMAIN 2: Index Test (All tests)
DOMAIN 2: Index Test (Antibody tests)
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 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
The reference standard does not incorporate the index test	Yes
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low 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?	Unclear
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
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		Unclear risk