Ruetalo 2020 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of current convalescent‐phase infection Design: Two‐group study to estimate sensitivity and specificity [1] Confirmed COVID patients [1a] Non‐hospitalised COVID‐patients (n = 49), 46 PCR+, 3 symptomatic close contacts [1b] one hospitalised, convalescent COVID patient (2 samples) [2] Healthy donors (n = 4); Group [2] excluded from our review as < 25 samples Group [1b] not included as no information on time pso or time post‐PCR+ [1a] 3 symptomatic close contacts excluded as not PCR‐confirmed Recruitment: Not stated Prospective or retrospective: Not stated Sample size: 55 (49) samples of which 46 (46) rt‐PCR positive COVID patients were eligible for our review Further detail: Inclusions [1a] Potential blood donors for convalescent plasma therapy after written consent at the Clinical Transfusion Medicine, Tübingen between April 04 and May 12, 2020 Older than 18 years old with a PCR‐confirmed diagnosis of SARS‐CoV‐2 (n = 46) or symptomatic and close contacts to positively diagnosed COVID‐19 patients (partners tested positive) [1b] Hospitalised, convalescent COVID patient [2] Healthy donors Exclusions not reported
Patient characteristics and setting	Setting: Convalescent (potential convalescent plasma donors) Location: Clinical Transfusion Medicine, Tübingen Country: Germany Dates: between April 04 and May 12, 2020 Symptoms and severity: non‐hospitalised, asymptomatic to a mild course of disease, cough (69%), fever (59%), limb pain and headache (35%), diarrhoea (10%), and loss of taste (10%). Now all convalescent Demographics: Age ranged from 19‐66 years (median 40 years); 24 male, 25 female Exposure history: Not stated
Index tests	Test name: [A] Euroimmun SARS‐CoV‐2‐ELISA (IgG) [B] S1 RBD SARS‐CoV‐2 (IgG, IgA, IgM) (test name not stated) [C] Elecsys anti‐SARS‐CoV‐2 *Additional assay (SARS‐COV‐2 DigiWest assay) excluded as not commercially available Manufacturer: [A] Euroimmun, Lübeck, Germany [B] Mediagnost [C] Roche Antibody: [A] IgG [B] IgG, IgA, IgM[C] Total antibody Antigen target: [A] S1‐based [B] [C] N‐protein Evaluation setting: All laboratory tests Test method: [A] ELISA [B] ELISA [C] ECLIA Timing of samples: The time from positive SARS‐CoV‐2 test to blood sampling was 14‐64 days (median 45 days). Samples used: Serum samples were stored at ‐80°C. Test operator: [A] Institute for Transfusion Medicine, University Hospital Tübingen, Tübingen, Germany [B] Mediagnost GmbH, Reutlingen, Germany [C] Institute for Medical Virology and Epidemiology of Viral Diseases, University Hospital Tübingen, Tübingen, Germany Definition of test positivity: [A] Ratios were classified as negative (< 0.8), borderline (≥ 0.8– < 1.1) and positive (≥ 1.1) [B] Ratios were classified as: negative (< 0.42), borderline (≥ 0.42‐0.7) and positive (≥ 0.7) for IgG; negative (< 0.33), borderline (≥ 0.33‐0.7) and positive (≥ 0.7) for IgA; negative (< 0.87), borderline (≥ 0.87‐1.47) and positive (≥ 1.47) for IgM [C] If the numeric COI result was ≥ 1.0, the serum was diagnosed as reactive, COI < 1.0 were attributed as non‐reactive. Blinding reported: Not stated Threshold predefined: yes
Target condition and reference standard(s)	Reference standard: PCR‐confirmed diagnosis of SARS‐CoV‐2 (n = 46) and three were symptomatic and close contacts to positively diagnosed COVID‐19 patients (partners tested positive), PCR threshold not stated. 3 COVID patients without PCR test not included in review Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: yes, prior to index test Incorporated index test: no
Flow and timing	Time interval between index and reference tests: The time from positive SARS‐CoV‐2 test to blood sampling was 14‐64 days (median 45 days). All patients received same reference standard: yes Missing data: yes (exclusion of groups [1b] and [2] and 3 patients from group [1a] from our review) Uninterpretable results: Not stated Indeterminate results: yes [A] n = 1 [B] n = 6 [C] n = 15 Unit of analysis: Patients
Comparative
Notes	Funding: This work was supported by grants to MS from the Baden‐Württemberg foundation (BW Stiftung), the Deutsche Forschungsgemeinschaft, the MWK Baden‐Würtemberg as well as by basic funding provided to MS by the University Hospital Tübingen and TÜFF Gleichstellungsförderung to K.A. (2563‐0‐0). Publication status: Pre‐print (not peer reviewed) Source: medRxiv pre‐print Author COI: The authors reported no conflict 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?	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?	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?	Yes
Were all patients included in the analysis?	No
Did all participants receive a reference standard?	No
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		High risk