Serre‐Miranda 2021 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of current acute‐phase infection and current convalescent‐phase infection Design: Two‐group study to estimate sensitivity and specificity [1] SARS‐CoV‐2‐infected inpatients (126 samples from 89 patients) [2] Pre‐pandemic controls (36 samples) [2a] Healthy (n = 25) and [2b] HIV and other viral diseases (n = 11) Recruitment: [1] Not stated [2] Matched samples were selected based on COVID‐19 patients’ sex and age Prospective or retrospective: [1] Prospective [2] Retrospective Sample size: 162 (126) samples Further detail: Inclusion: [1] Patients living in the Minho region of Portugal who were inpatients at Senhora da Oliveira Hospital (Guimarães) or Braga Hospital, admitted with COVID‐19 (diagnosed by RT‐qPCR at a reference laboratory; at least 2 positive RT‐qPCR results were obtained from each patient) [2] SARS‐COV‐2 non‐infected controls were selected from banked human plasma samples from 2 pre‐COVID‐19 pandemic studies conducted by the study authors (the first COVID‐19 case in Portugal was reported on 2 March 2020): [2a] a study with healthy individuals > 55 years old (samples collected between April 2019 and January 2020); [2b] a study with HIV‐infected patients on antiretroviral therapy (54–60 months; samples collected between January 2016 and August 2018). Matched samples were selected based on COVID‐19 patients’ sex and age.
Patient characteristics and setting	Setting: Hospital inpatients Location: Senhora da Oliveira Hospital (Guimarães, Portugal) or Braga Hospital (Braga, Portugal) Country: Portugal Dates: Not stated Symptoms and severity: Severe 32/89; non‐severe 57/89 Demographics: Age: median 71 [range 30;96] years; female 51/89 (57.3%) None of the COVID‐19 patients were HIV‐positive or had a history of organ transplantation. Exposure history: Not stated Non‐Covid group 1: [2a] Pre‐pandemic healthy Source: Banked human plasma samples from a pre‐COVID‐19 pandemic study with healthy individuals > 55 years old, samples collected between April 2019 and January 2020 Characteristics: Age: Median 71 [range 59 to 80] years; 13/25 (52.0%) female Non‐Covid group 2: [2b] Pre‐pandemic, other diseases Source: Banked human plasma samples from a pre‐COVID‐19 pandemic study with HIV‐infected patients on antiretroviral therapy, samples collected between January 2016 and August 2018 Characteristics: Age: Median 57 [range 33;72] years; 3/11 (27.3%) female
Index tests	Test name: [A] Abbott Architect anti‐SARS‐CoV‐2 IgG (no. 06R86) [B] EUROIMMUN ‐ anti‐SARS‐COV‐2 IgG (no. EI 2606‐9601 G) [C] EUROIMMUN ‐ anti‐SARS‐COV‐2 IgA (no. EI 2606‐9601 A) [D] Snibe Diagnostic ‐ MAGLUMI 2019‐nCoV IgG/IgM (no. 130219016M) [E] Cellex qSARS‐CoV‐ 2 IgG/IgM (no. WI5513C) [F] Getein One Step Test (no. CG2057) [G] Innovita Biological ‐ 2019‐nCoV Ab test [H] Liming Bio StrongStep1 IgM/IgG [I] Leccurate ‐ SARS‐CoV‐2 [J] Jiangsu Medomics Combined Ab [K] Render COVID‐19 IgM/IgG (no. K‐20‐RC‐CoV‐2) [L] SD Biosensor IgM/IgG Duo (no. Q‐NCOV‐01D) Manufacturer: [A] Abbott Architect [B] EUROIMMUN [C] EUROIMMUN [D] Snibe Diagnostic [E] Cellex [F] Getein [G] Innovita Biological [H] Liming Bio [I] Leccurate [J] Jiangsu Medomics [K] Render [L] SD Biosensor Antibody: [A] IgG [B] IgG [C] IgA [D] IgM/IgG [E] IgM/IgG [F] Total antibodies [G] IgM/IgG [H] IgM/IgG [I] IgM/IgG [J] IgM/IgG [K] IgM/IgG [L] IgM/IgG Antigen target: [A] N‐protein [B] S1‐protein [C] S1‐protein [D] S antigen and N‐protein [E] N and S‐proteins [F] N and S‐proteins [G] N and S‐proteins [H] Not specified [I] Not specified [J] Not specified [K] Not specified [L] N‐protein Evaluation setting: [A] ‐ [D] Laboratory tests used in lab [E] ‐ [L] POCT performed in lab (frozen plasma) Test method: [A] CLIA [B] ELISA [C] ELISA [D] CLIA [E] LFIA [F] LFIA [G] LFIA [H] LFIA [I] LFIA [J] LFIA [K] LFIA [L] LFIA Timing of samples: Days since symptom onset: Numbers varied per test: < 10 days: 12‐24 samples; 10–15 days: 12‐33 samples; 16–21 days: 20‐34 samples; > 21 days: 16‐35 samples Samples used: Plasma frozen at ‐80 degrees Celsius Test operator: C.S‐M., C.N., S.R., J.C‐G., C.S.S., N.V., P.B‐S. and P.A‐P. performed the experiments. Life and Health Sciences Research Institute (ICVS), School of Medicine, University of Minho, Braga, Portugal and ICVS/3B’s‐PT Government Associate Laboratory, Braga/Guimarães, Portugal. Definition of test positivity: Threshold not stated for [A] ‐ [E] (see Fig 2; according to the manufacturer's instructions) [A] Index (S/C) [B] Ratio (between 0.8 and 1.1 borderline) [C] Ratio (between 0.8 and 1.1 borderline) [D] Arbitrary units/mL [E]‐[L] Visual‐based Blinding reported: Not stated Threshold predefined: yes, tested according to the manufacturer’s instructions ([E] ‐ [L] visual‐based)
Target condition and reference standard(s)	Reference standard: [1] Diagnosed by RT‐qPCR at a reference laboratory; at least 2 positive RT‐qPCR results were obtained from each patient); threshold not stated Samples used: Not stated Timing of reference standard: Not stated Blinded to index test: yes, prior to index test Incorporated index test: no Definition of non‐COVID cases: [2] Pre‐pandemic Samples used: [2] Pre‐pandemic Timing of reference standard: [2] Pre‐pandemic Blinded to index test: yes, prior to index test Incorporated index test: no
Flow and timing	Time interval between index and reference tests: Not stated All patients received same reference standard: no Missing data: yes (not all patients tested with all tests, only 1 sample per time split used per patient) Uninterpretable results: Not stated Indeterminate results: Not stated (according to Fig 2, test [B] could have borderline results) Unit of analysis: Samples
Comparative
Notes	Funding: This work was funded by National funds, through the Foundation for Science and Technology (FCT) R4COVID ( 596694995), POCI‐01‐0145‐FEDER‐016428, UIDB/50026/2020 and UIDP/50026/2020; and by the projects NORTE‐01‐0145‐ FEDER‐000013 and NORTE‐01‐0145‐FEDER‐000023, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). CN, SR and NV are junior researchers under the scope of the FCT Transitional Rule DL57/2016. JC‐G is supported by an FCT PhD grant, in the context the Doctoral Program in Aging and Chronic Diseases (PhDOC; PD/ BD/137433/2018); CSS is supported by an FCT PhD grant, in the context of the Doctoral Program in Applied Health Sciences(PD/BDE/142976/2018). Publication status: Published paper Source: International Journal of Infectious Diseases Author COI: Getein kits were provided free of charge by the manufacturer. No other conflicts of interest reported
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?	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?	No
Were all patients included in the analysis?	No
Did all participants receive a reference standard?	Yes
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		High risk