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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] Confirmed COVID patients (209 samples from 35 patients) [2] Healthy close contacts (n = 21) Group [2] excluded from review as < 25 samples Recruitment: [1] From 23 January to 27 February 2020, 38 hospitalised COVID‐19 cases were consecutively recruited. Prospective or retrospective: Prospective Sample size: 56 (35) patients with 230 (209) samples of which 209 (209) samples were eligible for our review Sensitivity results reported for 70 (70) samples Further detail: Inclusion: Hospitalised COVID‐19 cases in two designated hospitals for COVID‐19 between 23 January and 27 February 2020 Exclusion: [1] One mild and two severe cases were transferred to other hospitals after hospitalisation in these two hospitals and were excluded from this study.
Patient characteristics and setting	Setting: Hospital inpatients Location: Two designated hospitals for COVID‐19, the Guangdong Seconded Provincial General Hospital and the First Hospital of Foshan in Guangdong, China Country: China Dates: 23 January to 27 February 2020 Symptoms and severity: 28 mild and 7 severe cases Demographics: Not stated Exposure history: Not stated
Index tests	Test name: [A] Cat. no. IEQ‐CoVS1RBD‐IgG [B] Cat. No. IE‐CoVS1RBD‐IgA [C] Cat. No. IE‐CoVS1RBD‐IgM Manufacturer: [A] ‐ [C] RayBiotech, GA, USA Antibody: [A] IgG [B] IgA [C] IgM Antigen target: [A] ‐ [C] RBD (from cat. No.) Evaluation setting: [A] ‐ [C] Laboratory tests performed in lab Test method: [A] ELISA [B] ELISA [C] ELISA Timing of samples: Serum samples were collected prospectively from cases every 3 days from hospitalisation until the date of discharge from hospital. Samples used: Serum Test operator: L.C., Z.L., H.L., R.Y., Z.P., H.X., X.Q., P.J., C.F., K.B., S.J., L.Z. and L.J. carried out the investigations. All from Guangdong Provincial Institute of Public Health, Guangdong Provincial Centre for Disease Control and Prevention, Guangzhou, China Definition of test positivity: According to the manufacturer's instructions, threshold not stated Blinding reported: Not stated Threshold predefined: yes, according to the manufacturer's instructions
Target condition and reference standard(s)	Reference standard: The laboratory‐confirmed case was defined as a case with respiratory specimens that tested positive for the SARS‐CoV‐2 by at least one of the following three methods: isolation of virus, positive results of real time reverse transcription polymerase chain reaction (rRT‐PCR) assay or a genome sequence that matched SARS‐CoV‐2. A commercial rRT‐PCR kit targeting the ORF1ab and N genes was used to detect SARS‐CoV‐2 RNA (DaAn Gene, Guangzhou, China. Cat.No.DA0931). Amplification was performed on an Applied Biosystems™ 7500 machine (ThermoFisher Scientific, USA). Specimens were considered positive for SARS‐CoV‐2 RNA if both ORF1ab and N gene target amplification curves were generated within 40 cycles. Samples used: Respiratory specimens 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: yes, group [2] excluded from review. No sensitivity data reported for test [C]; sensitivity results not available for all time points Uninterpretable results: Not stated Indeterminate results: Not stated Unit of analysis: Samples
Comparative
Notes	Funding: This work was supported by grants from the Guangdong Provincial Novel Coronavirus Scientific and Technological Project (2020111107001) and Guangzhou Novel Coronavirus Scientific and Technological Project (202008040004). Publication status: Published paper Source: Clinical Microbiology and Infection Author COI: All authors reported no conflicts of interest relevant to this article.
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?	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?	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?	Yes
Were all patients included in the analysis?	No
Did all participants receive a reference standard?	Yes
Were results presented per patient?	No
Could the patient flow have introduced bias?		High risk