Beavis 2020.

Study characteristics
Patient Sampling	Purpose: Diagnosis of acute and convalescent‐phase infection Design: Two‐group design to assess sensitivity and specificity: [1] COVID‐19 PCR+ve patients (n = 82) [2] COVID‐19 PCR‐ve patients (n = 86) Recruitment: unclear Prospective or retrospective: retrospective Sample size: 168(82) Further detail: Inclusion [1] Samples RT‐PCR‐positive for SARS‐CoV‐2. [2] Samples RT‐PCR‐negative for SARS‐CoV‐2. Ambulatory and pre‐pandemic. Exclusion: [1] [2] not stated
Patient characteristics and setting	Setting: Clinical Laboratories Location: University of Chicago Medicine Country: USA Dates: March to May 2020 Symptoms and severity: not stated Demographics: not stated Exposure history: not stated Non‐Covid group 1: COVID‐19 PCR‐ve patients Source: 70 samples collected from ambulatory patients at the University of Chicago from March to May 2020. 16 collected in early 2019, pre‐pandemic Characteristics: 28 of these patients had tested positive for common coronavirus strains (HKU1 n = 6, NL63 n = 10, OC43 n = 9, 229E n = 1, and both 229E and OC43 n = 1).
Index tests	Test name: [A] EUROIMMUN Anti‐SARS‐CoV‐2 ELISA IgG Assay [B] EUROIMMUN Anti‐SARS‐CoV‐2 ELISA IgA Assay Manufacturer: [A] [B] EuroImmun Antibody: [A] IgG [B] IgA Antigen target: [A] [B] S1 domain Evaluation setting: laboratory test Test method: Enzyme‐Linked Immunosorbent Assay (ELISA) Timing of samples: 0 to 49 days after PCR testing Samples used: serum or EDTA plasma Test operator: not stated Definition of test positivity: Ratio ≥ 1.1 positive, Ratio ≥ 0.8 to < 1.0 borderline, < 0.8 negative Blinding reported: unclear Threshold predefined: unclear
Target condition and reference standard(s)	Reference standard: RT‐PCR Samples used: Nasopharyngeal and nasal mid‐turbinate Timing of reference standard: not stated Blinded to index test: yes, prior Incorporated index test: no Definition of non‐COVID cases: RT‐PCR or pre‐pandemic Samples used: Nasopharyngeal and nasal mid‐turbinate Timing of reference standard: not stated Blinded to index test: yes, prior Incorporated index test: no
Flow and timing	Time interval between index and reference tests: 0‐49 days post‐PCR All patients received same reference standard: not stated Missing data: not stated Uninterpretable results: not stated Indeterminate results: borderline results were considered positive for analysis Unit of analysis: samples
Comparative
Notes	Funding: study was internally funded Publication status: Published paper Source: Journal of Clinical Virology Author COI: All authors declared no conflict 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?	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?	Unclear
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?		Unclear 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?	Unclear
Did all participants receive a reference standard?	Yes
Were results presented per patient?	No
Could the patient flow have introduced bias?		High risk