Chew 2020.

Study characteristics
Patient Sampling	Purpose: This study aimed to evaluate the diagnostic performance of the Abbott Architect SARS‐CoV‐2 IgG assay in COVID‐19 patients compared with pre‐pandemic controls. 2‐group study to estimate sensitivity and specificity for diagnosis of active disease and identification of previous disease Design: Two‐group study: [1] Symptomatic COVID‐19 patients selected on the basis of a positive SARS‐CoV‐2 rRT‐PCR from a respiratory sample (n = 177) [2] Negative controls were samples taken from patients prior to December 2019. These included patients with and without other positive serological tests (n = 163) Recruitment: Unclear whether all cases included ‐ "We prospectively identified confirmed COVID‐19 patients presenting at and admitted to our institution from 30th March 2020 to 15th May 2020". Prospective or retrospective: [1] prospective [2] retrospective Sample size: 340 (177) Further detail: [1] COVID‐19 patients selected on the basis of a positive SARS‐CoV‐2 rRT‐PCR from a respiratory sample. Patients who were asymptomatic at the time of PCR testing for contact screening purposes could not be stratified according to time from onset of illness and were excluded. [2] Unclear
Patient characteristics and setting	Setting: Hospital inpatient Location: National University Hospital, 5 Lower Kent Ridge Road, 11907, Singapore Country: Singapore Dates: 30th March 2020 to 15th May 2020 Symptoms and severity: Not stated, other than that patients who were asymptomatic at the time of PCR testing for contact screening purposes could not be stratified according to time from onset of illness and were excluded Demographics: Not stated Exposure history: Not stated Non‐Covid group 1: Pre‐pandemic controls Source: Negative controls were samples taken from patients prior to December 2019 Characteristics: Not stated. See comment Non‐Covid group 2: NA
Index tests	Test name: Abbott Architect SARS‐CoV‐2 IgG assay Manufacturer: Abbott Diagnostics, Chicago, USA Antibody: IgG Antigen target: IgG raised against the nucleocapsid protein of SARS‐CoV‐2 Evaluation setting: Laboratory, used in laboratory Test method: chemiluminescent immunoassay Timing of samples: COVID cases stratified according to time from onset of clinical illness to testing: (≤ 6 days, 81/177 7‐13 days, 39/177 14‐20 days 25/177, and ≥ 21 days 32/177) Samples used: Residual sera Test operator: Not stated Definition of test positivity: A signal/cut‐off (S/CO) ratio of >= 1.4 was interpreted as reactive and an S/CO ratio of < 1.4 was interpreted as non‐reactive. Also used alternate cut‐offs of 1.0 and 0.8 Blinding reported: Not stated Threshold predefined: A signal/cut‐off (S/CO) ratio of >= 1.4 was interpreted as reactive and an S/CO ratio of < 1.4 was interpreted as non‐reactive (Results also extracted for alternative lower cut‐off values. No for cutoffs 1.0 and 0.8)
Target condition and reference standard(s)	Reference standard: Two PCR assays were used during this time period (Fortitude, MirXES, Singapore, and cobas® SARS‐COV‐2, Roche Diagnostics, USA). No threshold reported Samples used: respiratory samples Timing of reference standard: Not stated Blinded to index test: Presumably, as cases selected on basis of reference test result Incorporated index test: No Definition of non‐COVID cases: None ‐ "negative samples collected prior to December 2019 were assumed to be negative as SARS‐CoV‐2 was first identified late in 2019". Samples used: pre‐pandemic Timing of reference standard: pre‐pandemic Blinded to index test: Yes, historical samples Incorporated index test: No
Flow and timing	Time interval between index and reference tests: Not stated All patients received same reference standard: No. For COVID cases, there were two different PCR assays in use while historical controls included patients with and without other positive serological tests and were assumed to be COVID‐negative. Missing data: Not stated Uninterpretable results: Not stated Indeterminate results: Not stated Unit of analysis: Patients
Comparative
Notes	Funding: No external funding was received for this study. Temasek Holdings Pte Ltd sponsored the laboratory testing kits used in this study. Publication status: Article in press; now published Source: Clinical Microbiology and Infection Author COI: One author (PT) received grants paid to the National University Hospital from Roche, Johnson & Johnson, Sanofi Pasteur, GlaxoSmithKline, and Shionogi. All other authors had no conflicts of interest to declare.
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?			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