Flinck 2021 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of current acute‐phase infection or current convalescent‐phase infection Design: Multi‐group study to estimate sensitivity and specificity [1] Confirmed COVID patients [1a] Inpatients (120 samples from 13 patients) for seroconversion [1b] Convalescent outpatients (n = 35) [2] Non‐COVID control samples [2a] Pre‐pandemic healthy (n = 161) [2b] Cross‐reaction samples (pre‐pandemic and current) (n = 43) Recruitment: [1a] Residual plasma samples from patients admitted to Tampere University Hospital or other communal hospitals in Fimlab Laboratories operation region [1b] serum samples from the COVID‐19 NAAT positive outpatients were traced and collected for evaluation. All patients had had respiratory tract symptoms [2a] Stored samples from the Chitosan study before the COVID‐19 era [2b] Follow‐up plasma/serum samples from patients with other diseases. EBV‐, HBcAb‐, and ANA‐positive samples collected in year 2019. RF‐positive samples collected in year 2017. The samples from other coronavirus and influenza A/B patients had been collected in April–May 2020. Prospective or retrospective: Retrospective Sample size: 359 (155) samples of which 244 (40) had extractable results for our review Further detail: Not stated
Patient characteristics and setting	Setting: [1a] Hospital inpatients [1b] Hospital outpatients Location: [1a] and [1b] Tampere University Hospital or other communal hospitals in Fimlab Laboratories operation region, Tampere Country: Finland Dates: Not stated Symptoms and severity: [1a] aggravated COVID‐19 respiratory tract symptoms, i.e. difficulty breathing [1b] All these patients had had respiratory tract symptoms including rhinitis, cough, sore throat, chest pain, and/or difficulty breathing, with or without fever Demographics: [1a] Age 55 years (median), range 20–79; 8/13 males [1b] Age 47 years (median), range 11–95; 12/35 males Exposure history: Not stated Non‐Covid group 1: [2a] Pre‐pandemic healthy Source: [2a] Part of the Chitosan study before the COVID‐19 era (cited study published in 2005) Characteristics: [2a] Apparently healthy adults [age 45 years (mean), range 32–65; 72 males] with mildly to moderately increased total cholesterol Non‐Covid group 2: [2b] Cross‐reaction panel Source: EBV‐, HBcAb‐, and ANA‐positive samples had been collected in year 2019, and RF‐positive samples in year 2017 before the COVID‐19 pandemic The samples from other coronavirus and influenza A/B patients had been collected in April–May 2020 Characteristics: Human coronavirus OC43: n = 13 Human coronavirus NL63: n = 2 Human coronavirus: 229E: n = 1 Human coronavirus OC43 and human bocavirus: n = 1 Influenza A virus: n = 5 Influenza A and B virus: n = 1 Acute Epstein‐Barr virus: n = 5 Hepatitis B core antibody positive: n = 5 Antinuclear antibody positive: n = 5 Rheumatoid factor positive: n = 5
Index tests	Test name: [A] Elecsys® Anti–SARS‐CoV‐2 test [B] LIAISON® SARS‐CoV‐2 S1/S2 IgG Manufacturer: [A] Roche Diagnostics GmbH, Mannheim, Germany [B] DiaSorin S.p.A., Saluggia, Italy Antibody: [A] Total antibodies [B] IgG Antigen target: [A] N‐protein [B] spike‐protein S1 and S2 antigens Evaluation setting: [A] and [B] Lab test performed in lab Test method: [A] Not stated (should be ECLIA) [B] Not stated (should be CLIA) Timing of samples: [1a] Not stated [3‐40 days pso (figure 1) for 83/120 samples] [1b] At least 16 days after positive NAAT Samples used: [1a] Residual EDTA plasma, stored −20 °C [1b] Residual plasma/serum samples [2a] Serum samples stored at −20 °C [2b] Plasma/serum samples Test operator: Lab personnel (Fimlab Laboratories, Tampere, Finland) Definition of test positivity: [A] COI = 1 (Fig 1) [B] Not stated (AU/mL) Blinding reported: Not stated Threshold predefined: Not stated
Target condition and reference standard(s)	Reference standard: [1] In‐house real‐time reverse‐transcription (RT)‐PCR test detecting E‐gene target sequence (using Charite Berlin protocol; Corman 2020); Allplex™ 2019‐nCoV Assay (Seegene Inc., Seoul, South Korea) detecting target sequences E, N, and RdRp; or Abbott RealTime SARS‐CoV‐2 Assay (Abbott Laboratories, Abbott Park, IL) detecting target sequences N and RdRp. The used RT‐PCR method had been chosen based on the availability. The primary COVID‐19 diagnosis was based on 1 RT‐PCR result. Samples used: Not stated Timing of reference standard: [1a] Not stated [1b] At least 16 days before index test Blinded to index test: yes, prior index test Incorporated index test: no Definition of non‐COVID cases: [2a] Pre‐pandemic [2b] Pre‐pandemic or not stated Samples used: [2a] Pre‐pandemic [2b] Pre‐pandemic or not stated Timing of reference standard: [2a] Pre‐pandemic [2b] Pre‐pandemic or not stated Blinded to index test: yes, prior index test Incorporated index test: no
Flow and timing	Time interval between index and reference tests: [1a] Not stated [1b] At least 16 days [2] Not stated All patients received same reference standard: No Missing data: yes (only 83 of 120 samples from seroconversion panel analysed) Uninterpretable results: Not stated Indeterminate results: Not stated Unit of analysis: [1a] Samples [1b] Patients [2a] Patients [2b] Patients
Comparative
Notes	Funding: The study was supported by Tampere Tuberculosis Foundation and Competitive State Research Financing of Expert Responsibility area of Tampere. Publication status: Published paper Source: Diagnostic Microbiology and Infectious Disease Author COI: No conflicts 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?	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?	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?	No
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?		High 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?	No
Did all participants receive a reference standard?	No
Were results presented per patient?	No
Could the patient flow have introduced bias?		High risk