Naaber 2020 [A].

Study characteristics
Patient Sampling	Purpose: Comparison of sensitivity of 7 commercial antibody tests to detect acute or convalescent‐phase SARS‐CoV‐2 infection Design: Multi‐group study to assess sensitivity and specificity of 7 commercial antibody tests [1] Confirmed COVID patients (n = 97) [1a] asymptomatic (n = 20) [1b] symptoms score 1‐6 (n = 43) [1c] symptoms score 7‐14 (n = 34) [2] Pre‐pandemic healthy controls (n = 100) Recruitment: [1] Recruited hospitalised and ambulatory patients, as well as healthy contacts of COVID‐19 patients selected randomly [2] Not stated Prospective or retrospective: [1] Unclear [2] Retrospective Sample size: 197 (97) samples of which 173 (73) were eligible for our review Further detail: [1] At least one‐week pso or post‐RT‐PCR +ve [2] anonymous serum samples collected before COVID‐19 pandemic and stored in SYNLAB Estonia from healthy persons for various health control laboratory tests Exclusions not stated Setting: Kurressaare Hospital inpatients, ambulatory patients and healthy contacts of COVID patients. Samples sent to SYNLAB Estonia central laboratory for testing Location: Kurressaare Hospital, Island of Saaremaa, Estonia Country: Estonia Dates: Serum samples collected between April 28 and May 07 2020 Symptoms and severity: Varied, 19.6% hospitalised, 44% recorded 1‐6 symptoms, 35% recorded 7+ symptoms, 20.6% asymptomatic. Demographics: Median age 59 years (21‐100 years), 32% male Exposure history: Not stated Non‐Covid group 1: [2] Pre‐pandemic, healthy persons Source: Anonymous serum samples collected before COVID‐19 pandemic (dates not stated), stored in SYNLAB Estonia Characteristics: Healthy, not screened for virus‐related antibodies
Patient characteristics and setting	Setting: Kurressaare Hospital inpatients, ambulatory patients and healthy contacts of COVID patients. Samples sent to SYNLAB Estonia central laboratory for testing Location: Kurressaare Hospital, Island of Saaremaa, Estonia Country: Estonia Dates: Serum samples collected between April 28 and May 07 2020 Symptoms and severity: Varied, 19.6% hospitalised, 44% recorded 1‐6 symptoms, 35% recorded 7+ symptoms, 20.6% asymptomatic Demographics: Median age 59 years (21‐100 years), 32% male Exposure history: Not stated Non‐Covid group 1: [2] Pre‐pandemic, healthy persons Source: Anonymous serum samples collected before COVID‐19 pandemic (dates not stated), stored in SYNLAB Estonia Characteristics: Healthy, not screened for virus‐related antibodies Non‐Covid group 2: NA Source: NA Characteristics: NA
Index tests	Test name: [A] MAGLUMI 2019‐nCoV IgG, SNIBE [B] SARS‐CoV‐2 ELISA IgG, EUROIMMUN [C] SARS‐CoV‐2 IgG, Abbott [D] Elecsys Anti‐SARS‐CoV‐2, Roche [E] EDI Novel Coronavirus COVID‐19 IgG ELISA [F] LIAISON SARS‐CoV‐2 S1/S2 IgG [G] STANDARDTM Q COVID‐19 IgM/IgG Duo Test Manufacturer: [A] SNIBE (Shenzhen New Industries Biomedical Engineering Co) [B] EUROIMMUN AG [C] Abbott Laboratories [D] Roche Diagnostics GmbH [E] Epitope Diagnostics Inc [F] DiaSorin S.p.A [G] SD BioSensor Inc Antibody: [A] IgG [B] IgG [C] IgG [D] Total antibody [E] IgG [F] IgG [G] IgG Antigen target: [A] not specified [B] S1 [C] N‐protein [D] N‐protein [E] N and S‐protein [F] S1 and S2 [G] N‐protein Evaluation setting: [A], [B], [C], [D], [E], [F] laboratory tests [G] rapid IgG test (POCT) Test method: [A] CLIA [B] ELISA [C] CMIA [D] ECLIA [E] ELISA [F] CLIA [G] Rapid chromatographic immunoassay Timing of samples: At least one‐week pso or post‐PCR +ve Median 28 (range 7–57) days to test 7‐14 days, n = 20 15‐30 days, n = 35 31‐57 days, n = 42 Samples used: Serum [1] Serum was separated and aliquoted before storage. All aliquots were stored at– 30˚ C and analysed within one month applying one freezing/thawing cycle before testing Test operator: Staff at SYNLAB Estonia Central Laboratory Definition of test positivity: [A] > 1 pos [B] ≥ 0.8‐ < 1.1 borderline, ≥ 1.1 pos [C] ≥ 1.4 pos [D] ≥ 1 pos [E] neg 0.9 x (neg control + 0.10), borderline if > 0.9‐1.1x(neg control + 0.10)?, pos 1.1 x (neg control + 0.10) [F] ≥ 12‐ < 15 borderline, ≥ 15 pos [G] Positive: any line in test window Blinding reported: Unclear Threshold predefined: Yes (Commercial tests were performed and interpreted according to manufacturer instructions).
Target condition and reference standard(s)	Reference standard: RT‐PCR Samples used: Not stated Timing of reference standard: Unclear Blinded to index test: Yes, performed prior to index test Incorporated index test: No Definition of non‐COVID cases: Pre‐pandemic healthy (date not stated) Samples used: Pre‐pandemic Timing of reference standard: Pre‐pandemic controls, healthy persons 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 ([1] rt‐PCR [2] Pre‐pandemic) Missing data: Nothing stated Uninterpretable results: Nothing stated Indeterminate results: yes (text mentioned 2 borderline results for test [B] and 4 borderline results reported for test [E]) Unit of analysis: Patients
Comparative
Notes	Funding: Funding acquired by Paul Naaber (first author), no more detail provided The study was supported by Estonian Research Council grants PRG377 (LH, PR, PP) and IUT34‐19 (PN, ES). SYNLAB Estonia provided support in the form of salaries for authors (PN, KH, JH, IE) and research materials, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Publication status: Published paper Source: PLOS One Author COI: The authors have read the journal’s policy and have the following competing interests: PN, KH, JH, IE are employees of SYNLAB Estonia. There were no patents, products in development or marketed products associated with this research to declare. This does not alter our adherence to PLOS One policies on sharing data and materials.
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?	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?	Yes
Could the patient flow have introduced bias?		High risk