DomBourian 2020 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of convalescent‐phase infection Design: Multi‐group study to estimate sensitivity and specificity [1] Confirmed COVID‐19 convalescent plasma samples (n = 102) [2] Non‐COVID samples (n = 126) [2a] Current non‐COVID, respiratory pathogen panel (RPP)‐positive samples (n = 20); [2b] Pre‐pandemic samples (n = 106) Recruitment: Not stated Prospective or retrospective: [1] and [2a] Unclear (possibly retrospective) [2b] Retrospective Sample size: 228 (102) samples Further detail: [1] SARS‐CoV‐2 PCR‐positive donors from the Children's Hospital Colorado CCP donor programme; eligible individuals for the CCP donor programme were confirmed PCR‐positive for SARS‐CoV‐2 and were symptom‐free for at least 14 days prior to plasma donation and met all standard blood donation criteria per FDA requirements. [2a] Residual samples from patients who had tested positive for one of the respiratory viral pathogens and who were confirmed to be PCR‐negative for SARS‐CoV‐2 [2b] Pre‐pandemic samples that were collected prior to November 2019
Patient characteristics and setting	Setting: Convalescent plasma donors Location: Children's Hospital Colorado's CCP donor programme, Aurora, Colorado Country: USA Dates: Children's Hospital Colorado's CCP donor programme was registered with the FDA as eligible to collect CCP on March 31, 2020. Symptoms and severity: Symptom‐free for at least 14 days Demographics: Not stated Exposure history: Not stated Non‐Covid group 1: [2a] Current cross reaction challenge Source: Not stated (current) Characteristics: Tested positive for one of the respiratory viral pathogens (adenovirus; human metapneumovirus [HMPV]; influenza virus A hemagglutinin [H] subtypes H1, H3, and 2009 H1N1; influenza virus B; respiratory syncytial virus; coronaviruses NL63, OC43, 229E, and HKU1; human rhinovirus/enterovirus; parainfluenza types 1–4; Bordetella pertussis; mycoplasma pneumonia; and chlamydophila pneumonia) Non‐Covid group 2: [2b] Pre‐pandemic Source: Source not stated; collected prior to November 2019 Characteristics: Not stated
Index tests	Test name: [A] EDI™ Novel Coronavirus COVID‐19 IgG ELISA kit [B] Euroimmun Anti‐SARS‐CoV‐2 ELISA (IgG) Manufacturer: [A] Epitope Diagnostics Inc. (EDI) (San Diego, CA) [B] Euroimmun (Lubeck, Germany) Antibody: [A] and [B] IgG Antigen target: [A] nucleocapsid antigen [B] S1 domain, including the receptor binding domain (RBD) of the SARS‐CoV‐2 spike‐protein Evaluation setting: [A] and [B] Lab test, unclear setting Test method: [A] and [B] ELISA Timing of samples: At least 14 days symptom‐free Samples used: Plasma or serum Test operator: Not stated Definition of test positivity: [A] For the EDI assay, positive, negative and borderline results were calculated based on the average optical density (OD450) value for the negative control assayed in triplicate for the specific assay. The positive and negative cut‐off values were calculated using the formula: positive cut‐off = 1.1 x (xNC + 0.18) and negative cut‐off = 0.9 x (xNC + 0.18), where xNC is the average OD450 of triplicate negative control OD values. Samples that had OD450 values that fell between positive and negative cut‐off values were reported as borderline. [B] The Euroimmun assay was interpreted based on the ratio of the sample OD450 to the calibrator OD450. Samples with a ratio of less than 0.8 were deemed negative, samples with a ratio of greater than 1.1 were positive, and OD450 values between 0.8 and 1.1 were reported as borderline. Blinding reported: Not stated Threshold predefined: Yes, for this study, the assays were used per the manufacturers' specifications.
Target condition and reference standard(s)	Reference standard: PCR, threshold not stated Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: Yes, prior index test Incorporated index test: No Definition of non‐COVID cases: [2a] PCR (unclear how many negative tests) [2b] Pre‐pandemic (before November 2019) Samples used: [2a] Not stated [2b] Pre‐pandemic Timing of reference standard: [2a] Not stated [2b] Pre‐pandemic Blinded to index test: Yes, prior index test 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: Not stated Uninterpretable results: Not stated Indeterminate results: [A] 6 borderline results [B] 6 borderline results Unit of analysis: Samples
Comparative
Notes	Funding: The Departments of Pediatrics and Pathology at the University of Colorado School of Medicine, and Children's Hospital Colorado Publication status: Published paper Source: Journal of Immunological Methods Author COI: All authors declared that they had 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?	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?	No
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?		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?	No
Were all patients included in the analysis?	No
Did all participants receive a reference standard?	Yes
Were results presented per patient?	No
Could the patient flow have introduced bias?		High risk