Chaudhuri 2020 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of current convalescent‐phase disease Design: Two‐group study to estimate sensitivity and specificity [1] Confirmed COVID patients (368 patients with 379 samples) [2] Pre‐pandemic non‐COVID samples (n = 184) Recruitment: [1] The participants for this study were derived from a longitudinal cohort of COVID‐19‐positive participants known as the Department of Biotechnology (DBT) India COVID‐19 Consortium cohort with ongoing recruitment from March 2020 at eight clinical sites in the Delhi‐National Capital Region, India. [2] Sera samples collected in the pre‐pandemic period (184 from pregnant women enrolled in a pregnancy cohort). Prospective or retrospective: [1] Department of Biotechnology(DBT) India COVID‐19 Consortium cohort: prospective [2] Retrospective (stored samples) Sample size: 563 (379) samples Further detail: [1] For longitudinal cohort study: i) Suspected COVID‐19 patients enrolled at the time of RT‐PCR testing at the screening centre and ii) RT‐PCR confirmed COVID‐19 positive patients admitted at one of the clinical sites For the present study: sera/plasma samples collected ≥ 20 days of illness or following RT‐PCR positivity [2] Sera samples collected in the pre‐pandemic period (before September 2019.) from pregnant women enrolled in a pregnancy cohort
Patient characteristics and setting	Setting: Convalescent, setting not stated Location: 8 clinical sites in the Delhi‐National Capital Region, India [Department of Biotechnology (DBT) India COVID‐19 Consortium cohort] Country: India Dates: from March 2020 Symptoms and severity: 83.7% symptomatic 16.3% asymptomatic (text says 14%?) Demographics: Not stated Exposure history: Not stated Non‐Covid group 1: [2] Pre‐pandemic healthy Source: Collected before September 2019 from pregnant women enrolled in a pregnancy cohort. Characteristics: 184/184 pregnant women
Index tests	Test name: [A] Diasorin LIAISON SARS‐CoV‐2 S1/S1 IgG CLIA [B] Covid Kavach IgG ELISA Manufacturer: [A] Diasorin [B] Zydus Antibody: [A] IgG [B] IgG Antigen target: [A] S1/S2 domains of the spike‐protein [B] specific antigenic epitope(s) of the inactivated virus in the Kavach assay were not defined Evaluation setting: [A] and [B] Lab tests performed in lab Test method: [A] Chemiluminescence assay (CLIA) [B] ELISA Timing of samples: 20‐72 days of illness in symptomatic or RT‐PCR positivity in asymptomatic individuals; duration of illness bimodal due to study design: The means of the sampling window distributions were 23.5 and 49.3 days respectively. Samples used: Serum or plasma Test operator: [A] and [B] Lab personnel Definition of test positivity: [A] The tests were considered positive when the IgG concentration was ≥ 15 AU/mL, negative when the concentration was < 12 AU/mL and equivocal when the concentration was > 12 and < 15 AU/mL. Equivocal samples were considered negative for sensitivity analysis. [B] The kit suggests interpretation of the results by a two‐pronged method, based on OD value and P/N (Positive/Negative Ratio). When both read‐outs are in agreement, then the sample is considered positive or negative. The manufacturer’s instruction does not mention interpretation for samples with a read‐out not in agreement for the two criteria. We considered such results negative. Blinding reported: Not stated Threshold predefined: [A] IgG concentration (AU/mL) as per manufacturer's instructions [B] OD value and P/N (Positive/Negative Ratio) as per manufacturer's instructions
Target condition and reference standard(s)	Reference standard: The testing by RT‐PCR was done at an approved laboratory as per the National Testing Strategy of India; threshold not reported Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: Yes, prior Incorporated index test: No Definition of non‐COVID cases: Pre‐pandemic Samples used: Pre‐pandemic Timing of reference standard: Pre‐pandemic Blinded to index test: Yes, prior Incorporated index test: No
Flow and timing	Time interval between index and reference tests: Not stated All patients received same reference standard: No Missing data: The specificity of DiaSorin could not be evaluated due to limited availability of pre‐pandemic negative sera. Uninterpretable results: Not stated Indeterminate results: [A] Seven samples were reported as indeterminate by DiaSorin CLIA. Equivocal samples were considered negative for sensitivity analysis. [B] 6 samples were indeterminate in Zydus Kavach test and excluded from the study; and 23 (not 25, corrected by author) samples were positive only by one condition (cut‐off, P/N ratio) by Zydus Kavach. Unit of analysis: Samples (11 patients with 2 samples)
Comparative
Notes	Funding: We deeply thank the Department of Biotechnology, Government of India for supporting the consortium. We are grateful to the leadership and administration of all partner institutions in the consortium for their help and support. We thank all the clinical, laboratory and data management staff for their contributions to this work and the consortium at large. Publication status: Published paper Source: Journal of Clinical Virology Author COI: No 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?	No
Did the study avoid inappropriate exclusions?	No
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?			Low concern
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?	No
Were all patients included in the analysis?	Yes
Did all participants receive a reference standard?	No
Were results presented per patient?	No
Could the patient flow have introduced bias?		High risk