Padoan 2020b [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of acute‐phase infection and antibody kinetics over time Design: Single‐group study to estimate sensitivity: [1] adult patients with PCR‐confirmed COVID‐19 (total N was not reported, 51 assessed for IgM and 19 assessed for IgA; any overlap between patient groups was not reported) The report contained two groups of COVID‐19 patients, one was assessed for IgM using CLIA and the other for IgA using ELISA. There was no non‐COVID‐19 or healthy control group. [1] Severely sick adult COVID‐19 (rRT‐PCR‐confirmed) patients longitudinally assessed for IgM using CLIA (n = 51) [2] Severely sick adult COVID‐19 (rRT‐PCR‐confirmed) patients longitudinally assessed for IgA using ELISA (n = 19) Recruitment: Unclear Prospective or retrospective: Not stated Sample size: Unclear; 51 reported for IgM and 19 for IgA; overlap not reported Further detail: No further details
Patient characteristics and setting	Setting: Not stated; 'patients', presumably inpatient as serial testing Location: University‐Hospital of Padova Country: Italy Dates: Not stated Symptoms and severity: Discussion described patients as 'severely sick' Demographics: n = 51; 37, 72.5% male; mean age, men 69.1 y (SD 13.5), range 22–89 y; women 62.6 y (SD 11.0), range 41–82 y; n = 19; 15, 79% male; mean age, men 65.4 y (SD 14.5), range 22–81 y; women 63.7 y (SD 7.8) range 53–70 y Exposure history: Not stated
Index tests	Test name: [A] MAGLUMI 2000 Plus [B] ELISA Manufacturer: [A] Not stated (manufacturer was SNIBE diagnostics) [B] Euroimmun Medizinische Laboradiagnostika, Luebeck, Germany Antibody: [A] IgM (IgG also measured, limited details in supplementary information) [B] IgA (IgG also measured, results not reported) Antigen target: [A] S‐antigen and N‐protein [B] S1‐specific IgA and IgG Evaluation setting: Laboratory Test method: [A] chemiluminescent (CLIA) assay [B] ELISA Timing of samples: from the onset of symptoms (fever) to 6 weeks after Samples used: Not stated Test operator: Not stated Definition of test positivity: 1. CLIA IgM cut‐off: 1.0 kAU/L 2. ELISA IgA cut‐off: ratio ≥ 1.1 Blinding reported: Not stated Threshold predefined: Yes, as previously published
Target condition and reference standard(s)	Reference standard: rRT‐PCR, no further details Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: Not stated Incorporated index test: Not stated
Flow and timing	Time interval between index and reference tests: Not stated All patients received same reference standard: Yes Missing data: Unclear; data for all reported patients seemed to be used to estimate mean titres over time. A subgroup of 18 patients with more than 3 serial measurements was also reported. The number of patients contributing data from day 0 to 23 in Tabl 1 was not reported, however, at each time point, results were presented for fewer (16‐58%) than the total 19 participants for the IgA ELISA and total 51 participants for IgM CLIA. Uninterpretable results: Not stated Indeterminate results: Not stated Unit of analysis: Patients; however reported time periods were short (2‐day span), therefore, when results were combined to allow analysis per week post‐symptom onset, patients could contribute more than one sample per week.
Comparative
Notes	Funding: Not stated, except: "We acknowledge the support of Euroimmun Medizinische Laboradiagnostika, Luebeck, Germany for kindly supplying the reagents without any influence in study design and data analysis." Publication status: Published paper Source: International Journal of Clinical Chemistry Author COI: Not stated
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?			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?	Unclear
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?	Yes
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?		Unclear risk