Adams 2020.

Study characteristics
Patient Sampling	Purpose: Diagnosis of acute and convalescent‐phase COVID‐19 infection Design: Two‐group design with sensitivity and specificity [1] Confirmed (RT‐PCR‐positive) COVID‐19 (n = 270 samples from 124 patients) [2] Pre‐pandemic bio‐banked serum samples from three sources (from 2018 to pre‐December 2019) (n = 564 samples) Recruitment: Unclear Prospective or retrospective: Cases prospectively enrolled Sample size: 834 (270) samples Further detail: Not further described
Patient characteristics and setting	Setting: Unclear (early validation conducted on inpatient samples but not clear for final validation study which included asymptomatic cases) Location: South West London Pathology Laboratory at St George’s University Hospital, London Country: UK Dates: Not stated; conducted subsequent to 26 March 2020 Symptoms and severity: 209/270 samples (77%) from 90/124 patients reporting symptoms of COVID‐19 61/270 samples (23%) from 34/124 individuals who were asymptomatic at first swab collection Demographics: age: range, 26‐88 years Sex: 74/124 (60%) male Exposure history: Not stated Non‐Covid group 1: Pre‐pandemic Source: Hospital controls from 2018 to pre‐December 2019. Bio‐banked serum samples from Liverpool School of Tropical Medicine, Mologic, and St George’s University of London Characteristics: Not stated
Index tests	Test name: IgG COVID‐19 ELISA Manufacturer: Mologic Antibody: IgG Antigen target: NP and S2 antigens Evaluation setting: Laboratory‐based (South West London Pathology (SWLP) microbiology laboratory at St George’s, University Hospitals NHS Foundation Trust (SGHFT)) Test method: ELISA Timing of samples: [1] post‐symptom onset (range 1 to 54 days based on Fig 3) < 7: n = 16 (6%) (not reported but back‐calculated from Tabl 2B) >= 7‐14, n = 32, 12% >= 14‐21, n = 45, 17% >= 21‐28, n = 58, 21% >= 28‐35, n = 30, 11% >= 35, n = 29, 11% asymptomatic, n = 60, 22% [2] previously in hospital. Timing of samples: [1] post‐symptom onset (range 1 to 54 days based on Fig 3) < 7: n = 16 (6%) >= 7‐14, n = 32, 12% >=14 ‐ 21, n = 45, 17% >= 21‐28, n = 58, 21% >= 28‐35, n = 30, 11% >= 35, n = 29, 11% asymptomatic, n = 60, 22% Samples used: serum Test operator: Not stated Definition of test positivity: results were considered positive 'if they were 10% above the cut off value'; multiple thresholds reported in Suppl Appendix Blinding reported: Unclear Threshold predefined: Unclear
Target condition and reference standard(s)	Reference standard: RT‐PCR; Altona Diagnostics RealStar®SARS‐CoV‐2 RT‐PCR Kit detecting S and E genes from extracted RNA Samples used: Respiratory samples Timing of reference standard: Not reported Blinded to index test: Yes Incorporated index test: no Definition of non‐COVID cases: Pre‐pandemic controls Samples used: bio‐banked serum samples Timing of reference standard: Pre‐pandemic controls Blinded to index test: Yes Incorporated index test: No
Flow and timing	Time interval between index and reference tests: Serum samples obtained between 0 to 42 days post‐RT‐PCR n = 53, 0‐7 days. n = 215, ≥ 8 days. n = 197, ≥ 10 days. n = 159, 14‐42 days. All patients received same reference standard: No (different for cases and controls) Missing data: None reported Uninterpretable results: None reported Indeterminate results: None reported Unit of analysis: Samples mainly (with a few results by patients)
Comparative
Notes	Funding: UK Department for International Development and Wellcome Trust Publication status: Pre‐print (not peer reviewed) Source: medRxiv Author COI: COI declared: SK is a member of the Scientific Advisory Committee for Foundation for Innovative New Diagnostics (FIND) a not‐for‐profit that produces global guidance on affordable diagnostics. The views expressed here are personal opinions and do not represent the recommendations of FIND.
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?	Unclear
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?	Unclear
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		High risk