Chan 2020a.

Study characteristics
Patient Sampling	Purpose: Diagnosis of current acute and convalescent‐phase infection Design: Multi‐group study to assess sensitivity and specificity [1] Covid subjects (n = 144) [1a] Admitted PCR‐positive samples (n = 78) for clinical performance study [1b] Archived PCR‐positive samples (n = 66) for method comparison study [2] Non covid subjects (n = 130) [2a] non‐SARS‐CoV‐2 respiratory viral samples (n = 25) [2b] Other viral positive samples (n = 52) [2c] Pre‐pandemic samples (n = 53) [1b] excluded from review as no time pso or post‐PCR+ reported. Recruitment: [1a] Admitted PCR‐positive patients who had routine metabolic profiles and serologies ordered for clinical care [1b] Archived samples from the validation studies for the EuroImmun Ab assay [2a] [2b] Not stated, likely samples from storage [2c] Pre‐pandemic samples (41 from a reference range study prior to 2018 and 12 from a banked respiratory viral panel from early 2019) Prospective or retrospective: Retrospective Sample size: 274 (144) of which 208 (78) were eligible for review Further detail: Inclusion: [1a] PCR‐positive for SARS‐CoV‐2 admitted to hospital [1b] Archived PCR‐positive samples from the validation studies for the EuroImmun Ab assay [2a] Positive for non‐SARS‐CoV‐2 respiratory infection (coronaviruses: HKU1 n = 5, NL63 n = 7, OC43 n = 7, 229E n = 2, OC43 + 229E CV n = 1, Rhinovirus n = 2) [2b] Positive for other viruses (HIV n = 20, HepB n = 15, HCV n = 17) [2c] Pre‐pandemic (41 from a reference range study prior to 2018 and 12 from a banked respiratory viral panel from early 2019) Exclusion: [1a] [1b] [2a] [2b] [2c] Not stated
Patient characteristics and setting	Setting: [1a] Hospital inpatients Location: Chemistry and Immunology Laboratories, University of Chicago Hospitals, Chicago, IL Country: USA Dates: Not stated Symptoms and severity: [1a] All hospitalised Demographics: Not stated Exposure history: Not stated Non‐Covid group 1: [2a] non‐SARS‐CoV‐2 respiratory viral samples Source: University of Chicago Hospitals, Chicago, IL; time not stated Characteristics: HKU1 CV n = 5, NL63 CV n = 7, OC43 CV n = 7, 229E CV n = 2, OC43 CV + 229E CV n = 1, Rhinovirus n = 2 Non‐Covid group 2: [2b] Other viral positive samples [2c] Pre‐pandemic samples Source: [2b] University of Chicago Hospitals, Chicago, IL; time not stated [2c] University of Chicago Hospitals, Chicago, IL, 41 prior to 2018, 12 from early 2019 Characteristics: [2b] HIV n = 20, HepB n = 15, HCV n = 17 [2c] Not stated (41 from a reference range study prior to 2018 and 12 from a banked respiratory viral panel from early 2019)
Index tests	Test name: [A] Elecsys anti‐SARS‐CoV‐2 antibody assay [B] EuroImmun IgG antibody assay (anti‐SARS‐CoV‐2 ELISA) Manufacturer: [A] Roche diagnostics [B] Euroimmun Antibody: [A] Total antibody [B] IgA/IgG Antigen target: [A] Nucleocapsid protein [B] Not stated Evaluation setting: Laboratory test used in laboratory setting Test method: [A] ECLIA [B] ELISA Timing of samples: [1a] 0‐13 days post‐PCR + (n = 40) >= 14 days post‐PCR + (n = 38) Samples used: Serum and plasma Test operator: Clinical chemistry staff at the University of Chicago Definition of test positivity: [A] COI >= 1.0 positive, COI < 1.0 negative [B] Not stated Blinding reported: Unclear Threshold predefined: Yes
Target condition and reference standard(s)	Reference standard: RT‐PCR, threshold not stated Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: Yes Incorporated index test: No Definition of non‐COVID cases: [2a] [2b] not stated, possibly pre‐pandemic [2c] pre‐pandemic Samples used: [2a] [2b] unclear [2c] pre‐pandemic Timing of reference standard: [2a] [2b] unclear [2c] pre‐pandemic Blinded to index test: yes, prior to index test Incorporated index test: no
Flow and timing	Time interval between index and reference tests: [1a] 0‐13 days post‐PCR + (n = 40) >= 14 days post‐PCR + (n = 38) All patients received same reference standard: No Missing data: [1b] excluded from review as well as 40 samples from [1a] < 14 days post‐PCR+ Uninterpretable results: Not stated Indeterminate results: Not stated, no indeterminate threshold Unit of analysis: Unclear
Comparative
Notes	Funding: Not stated Publication status: Published paper Source: American Journal of Clinical Pathology Author COI: Not stated
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?	No
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?	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?	No
Were results presented per patient?	Unclear
Could the patient flow have introduced bias?		High risk