Tang 2020 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of acute and convalescent‐phase infection using three commercial SARS‐CoV‐2 IgG assays Design: Multiple‐group study estimating sensitivity and specificity: [1] residual serum samples from patients with laboratory‐confirmed COVID‐19 infection and physician ordered completed blood count (n = 48, providing 103 samples) [2] PCR‐negative COVID‐19 suspects (n = 80); [3] pre‐pandemic serum (n = 50) [4] PCR‐negative, with other confirmed coronavirus (HKU1, NL63, and 229E) (n = 5) or influenza A or B (n = 4) [5] serum from patients with potentially interfering antibodies (n = 14; CMV IgG (n = 5), EBV VCA IgG (n = 3) or IgM (n = 3) or both (n = 2), RF+ (n = 1)) Recruitment: Not stated Prospective or retrospective: Retrospective Sample size: 256 (103) Further detail: No further details
Patient characteristics and setting	Setting: Unclear; 'a majority of our patient population (were) hospitalised' Location: Barnes Jewish Hospital, St. Louis, MO Country: USA Dates: No information Symptoms and severity: No information; 'majority' hospitalised Demographics: No information Exposure history: No information Non‐Covid group 1: Presumed negative controls Source: Source unclear Characteristics: No information
Index tests	Test name: [A] Abbott SARS‐CoV‐2 IgG assay [B] EUROIMMUN SARS‐CoV‐2 IgG assay [C] Roche Elecsys Anti‐SARS‐CoV‐2 Manufacturer: [A] Abbott diagnostics [B] EUROIMMUN [C] Roche Antibody: [A] and [B] IgG [C] total Ab Antigen target: [A] undisclosed epitope of the SARS‐CoV‐2 nucleocapsid protein [B] S1 domain of viral spike‐protein [C] nucleocapsid protein from SARS‐CoV‐2 Evaluation setting: Laboratory‐based assays Test method: [A] CLIA [B] ELISA [C] CLIA Timing of samples: Day 0 to >= 14 days pso Timing of samples: Day 0 to >= 14 days pso Samples used: Discussion stated plasma; PCR+ samples collected in EDTA Vacutainer tubes; controls were either stored or recent specimens (source unclear). Test operator: Not stated Definition of test positivity: [1] ratio ≥ 1.4 [B] positive = ratio ≥ 1.1 ; borderline = ratio < 1.1 to ≥ 0.8; results extracted considering borderline results +ve or ‐ve [C] ratio of specimen electrochemiluminescent signal to calibrator; cut‐off index (ratio) ≥ 1.0. Blinding reported: Not stated Threshold predefined: as per manufacturer
Target condition and reference standard(s)	Reference standard: RT‐PCR using one of three platforms due to reagent shortages: [1] Quidel Lyra RT‐PCR assay (majority) [2] Xpert Xpress SARS‐CoV‐2 molecular assay (Cepheid) [3] Simplexa COVID‐19 Direct Assay using a LIAISON MDX (Diasorin) Samples used: nasopharyngeal (NP) swabs, oropharyngeal (OP) swabs, or lower respiratory tract specimens (only latter used with Diasorin Simplexa) Timing of reference standard: varying times from symptom onset Blinded to index test: Not stated Incorporated index test: No Definition of non‐COVID cases: RT‐PCR for COVID‐19 suspects (n = 80) and for other infection samples (5 with other CoV); Unclear reference for other interfering antibody samples (n = 14); Pre‐pandemic for remaining 50 Samples used: Serum Timing of reference standard: Not stated Blinded to index test: Not stated Incorporated index test: No
Flow and timing	Time interval between index and reference tests: Reported as 0 to >= 14 days after positive PCR All patients received same reference standard: Yes; all RT‐PCR (different kits) Missing data: None reported Uninterpretable results: None reported Indeterminate results: For EUROIMMUN ELISA, borderline results were initially considered positive (main text) and reported as negative in Supplementary Information. Unit of analysis: Samples; patients per week (all 48 reported at >= 14 days pso)
Comparative
Notes	Funding: None declared Publication status: Accepted manuscript and subsequently research letter Source: Clinical Chemistry Author COI: Employment or leadership: A.M. Gronowski, Clinical Chemistry, AACC. Consultant or Advisory Role: N.W. Anderson, Diasorin Molecular
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?			Low concern
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?	Unclear
The reference standard does not incorporate the 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?	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?	Unclear
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		Unclear risk