Bundschuh 2020.

Study characteristics
Patient Sampling	Purpose: The aim of this study was to evaluate the effectiveness of the EDI ELISA test for the detection of SARS‐CoV‐2 IgM and IgG antibodies in human plasma. 3‐group study to estimate sensitivity and specificity for diagnosis of active disease Design: Three‐group study: [1] RT‐PCR‐positive COVID‐19 patients admitted for treatment at two tertiary hospitals (n = 64) [2] Healthy blood donors (pre‐pandemic, n = 200) [3] Medical intensive care patients (pre‐pandemic, n = 256) Recruitment: [1] SARS‐CoV‐2 RT‐PCR (from respiratory specimens) confirmed COVID‐19 patients that were treated in one of the two tertiary care hospitals. Blood samples for clinical routine that were sent to central laboratory were included in the present study (frozen, leftover plasma). [2] First 200 consecutive EDTA plasma samples from our previously described cohort of healthy blood donors [3] 256 consecutive baseline EDTA plasma samples of patients admitted to the medical intensive care unit of the Konventhospital Barmherzige Brueder Linz, Austria Prospective or retrospective: [1] Unclear [2] and [3] retrospective Sample size: 520 (64) patients with 560 (104) samples Further detail: [1] All COVID‐19 patients admitted for treatment at two tertiary hospitals. Criteria unclear [2] Healthy blood donors. [3] Medical intensive care patients
Patient characteristics and setting	Setting: Hospital inpatients, two tertiary care hospitals Location: Konventhospital Barmherzige Brueder Linz and Ordensklinikum Linz Barmherzige Schwestern in Linz, Austria Country: Austria Dates: Between 15th of March 2020 and 10th of April 2020 Symptoms and severity: Not stated Demographics: 64 patients (53 males, 11 females), median age 65 years (range 14–95, IQR 56–87, years) Exposure history: Not stated Non‐Covid group 1: [2] Healthy blood donors Source: Recruited at the Red Cross organisation in Linz, Austria from January 31st to February 13th 2008 Characteristics: 3% immune‐compromised Non‐Covid group 2: [3] Intensive care patients Source: Intensive care unit of the Konventhospital Barmherzige Brueder Linz Characteristics: Intensive care patients
Index tests	Test name: EDI Novel Coronavirus COVID‐19 IgM and IgG ELISA kit Manufacturer: Epitope Diagnostics Inc. Antibody: IgM, IgG Antigen target: nucleocapsid protein of SARS‐CoV‐2 Evaluation setting: Laboratory (ELISA), used in laboratory Test method: Enzyme‐Linked Immunosorbent Assay (ELISA) Timing of samples: < 5 days‐22 days after symptom onset (COVID‐19 patients). Results were reported for 4 time bands Samples used: Plasma Test operator: Laboratory staff Definition of test positivity: Single run: If the patient sample OD (optical density) was below the negative cut‐off the result was reported negative (‐); If the patient sample OD was above the negative cut‐off but below the positive cut‐off the result was reported borderline (+‐); If the patient sample OD was above the positive cut‐off the patient was reported as positive (+). Blinding reported: Not stated Threshold predefined: following the manufacturers instruction
Target condition and reference standard(s)	Reference standard: RT‐PCR Samples used: respiratory specimens Timing of reference standard: Not stated Blinded to index test: Yes, done prior index test Incorporated index test: No. Different specimens and tests Definition of non‐COVID cases: [2] and [3] pre‐pandemic Samples used: [2] and [3] pre‐pandemic Timing of reference standard: [2] and [3] pre‐pandemic Blinded to index test: Yes, done prior index test Incorporated index test: No, pre‐pandemic samples
Flow and timing	Time interval between index and reference tests: Not stated All patients received same reference standard: Yes Missing data: Not stated Uninterpretable results: Not stated Indeterminate results: If the patient sample was above the negative cut‐off but below the positive cut‐off the result was reported borderline ‐ these have not been extracted to the 2 x 2 sensitivity/specificity tables, and have accordingly been subtracted from group denominators. Unit of analysis: Samples
Comparative
Notes	Funding: None reported Publication status: Published paper Source: Clinica Chimica Acta Author COI: The authors declared that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Yes
Was a case‐control design avoided?	No
Did the study avoid inappropriate exclusions?	Yes
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?	No
Were results presented per patient?	No
Could the patient flow have introduced bias?		High risk