Rode 2021 [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of current acute‐phase infection Design: Single‐group study to estimate sensitivity [1] Confirmed COVID patients (n = 21, 60 samples) Recruitment: Randomly selected hospitalised adult patients (consecutive sera analysed) Prospective or retrospective: Prospective Sample size: 60 (60) samples Further detail: Inclusion: Subjects who had positive RT‐PCR and were hospitalised Exclusion: Test group ‐ PCR‐negative samples
Patient characteristics and setting	Setting: Hospital inpatients Location: University Hospital for Infectious Diseases “Dr. Fran Mihaljević”, Mirogojska 8, 10000 Zagreb. Country: Croatia Dates: Not stated Symptoms and severity: The most common symptoms were cough (95.2%), fever (90.5%), fatigue (42.9%) and shortness of breath (42.9%). Pulmonary opacities showed in 76.2% of patients. Severity ‐ mild, moderate and severe; Mild disease 5 (23.8%) Moderate disease 10 (47.6%) Severe disease 6 (28.6%) Demographics: Age median (range), years 56 (26–81); male/female 13 (61.9%)/8 (38.1%); comorbidity 10 (47.6%) Exposure history: Not stated
Index tests	Test name: [A] Anti‐SARS‐CoV‐2 IgA ELISA [B] Anti‐SARS‐CoV‐2 IgG ELISA [C] SARS‐CoV‐2 IgM/IgG Antibody Assay Kit Manufacturer: [A,B] Euroimmun, Germany [C] Maccura Biotechnology Co., Ltd. Antibody: [A] IgA, [B] IgG [C] IgM and IgG Antigen target: [A,B] S1 antigen [C] N/S antigen Evaluation setting: [A,B] Laboratory [C] POCT performed in lab Test method: [A,B] ELISA and [C] Collodial Gold Timing of samples: Range 0‐22 days post‐symptom onset: 0‐3 days pso: n = 11, 4‐7 days pso: n = 17, 8‐11 days pso: n = 18, >= 12 days from onset of illness: n = 14 Samples used: Serum Test operator: Laboratory personnel Definition of test positivity: [A,B] The antibody levels were determined by calculating the extinction ratio of the patient samples (S) over the cut‐off calibrator value (CO; S/CO). Cut‐off not stated [C] A clearly visible coloured quality control band and detection line, either IgG or IgM, were deemed positive for anti‐SARS‐CoV‐2 antibodies. The final results were always read by two independent investigators. Blinding reported: Not stated (no as only COVID cases included) Threshold predefined: yes by the manufacturer
Target condition and reference standard(s)	Reference standard: RT‐qPCR Roche Total Nucleic Acid Isolation kit on a Roche MagnaPure LC 2.0 (Roche, Germany) According to the WHO‐recommended Charité protocol, utilising the E and RdRP gene targets on an Applied Biosystems 7500 real‐time thermocycler (Applied Biosystems, USA), 5 μL of RNA was used for the detection of SARS‐CoV‐2. Threshold not stated Samples used: Combined nasopharyngeal and oropharyngeal swabs 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: Not stated All patients received same reference standard: Yes Missing data: Not stated Uninterpretable results: Not stated Indeterminate results: Not stated Unit of analysis: Samples (Eleven patients had 2 consecutive sera, 6 had 3 sera, and 3 had 4 sera and for one patient, 8 samples were tested)
Comparative
Notes	Funding: None stated Publication status: Published paper Source: European Journal of Clinical Microbiology & Infectious Diseases Author COI: The authors declared that they had 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?	Yes
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?	No
If a threshold was used, was it pre‐specified?	Yes
Could the conduct or interpretation of the index test have introduced bias?		High 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?	Yes
Did all participants receive a reference standard?	Unclear
Were results presented per patient?	No
Could the patient flow have introduced bias?		High risk