Pollan 2020.

Study characteristics
Patient Sampling	Purpose: Two‐group study to estimate sensitivity and specificity for diagnosis of acute Covid Design: [1] PCR‐confirmed Covid‐19 cases with serum samples (n = 82) [2] Pre‐pandemic serum samples for diagnosis of other pathogens (n = 42) [Study was reported as part of a wider seroprevalence survey; a second validation study of another immunoassay was also reported but not eligible for inclusion] Recruitment: Not stated Prospective or retrospective: Unclear; appeared to be retrospective Sample size: 124 (82); 66 (24) eligible for review Further detail: No further details reported
Patient characteristics and setting	Setting: Not stated Location: Not stated; validation study conducted by Spanish National Centre for Microbiology, Madrid Country: Spain Dates: Not stated Symptoms and severity: Not stated Demographics: Not stated Exposure history: Not stated Non‐Covid group 1: Pre‐pandemic serum samples for diagnosis of other pathogens Source: Samples collected before December 8th 2019 Characteristics: Not stated
Index tests	Test name: SARS‐CoV‐2 IgG for use with ARCHITEC Manufacturer: Abbott Laboratories, IL, USA Antibody: IgG Antigen target: SARS‐CoV‐2 nucleoprotein Evaluation setting: Laboratory, used in laboratory Test method: Chemiluminescent microparticle immunoassay Timing of samples: All PCR+ were >= 10 days pso (n = 82), 58 (71%) >= 14 days pso Samples used: Serum samples Test operator: Not stated Definition of test positivity: Index S/C threshold of 1.4 Blinding reported: Not stated Threshold predefined: Yes, as per manufacturer
Target condition and reference standard(s)	Reference standard: RT‐PCR Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: Presumed yes as reference standard performed before index test Incorporated index test: No Definition of non‐COVID cases: Pre‐pandemic Samples used: NA (pre‐pandemic) Timing of reference standard: NA (before December 8th 2019) Blinded to index test: Yes 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: Nothing mentioned Uninterpretable results: Nothing mentioned Indeterminate results: Nothing mentioned Unit of analysis: Not clear, did not state 1 sample per patient
Comparative
Notes	Funding: Spanish Ministry of Health and the Institute of Health Carlos III, in collaboration with the health services of the Spanish regions The funders facilitated data acquisition but had no role in the design, analysis, interpretation, or writing. The first three authors had full access to all the data. The first five authors and the senior author (RY) had final responsibility for the decision to submit for publication. Publication status: Published paper Source: Lancet Author COI: Authors declared no competing interests.
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?	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?	Unclear
Did all participants receive a reference standard?	Yes
Were results presented per patient?	Unclear
Could the patient flow have introduced bias?		High risk