Liu 2021.

Study characteristics
Patient Sampling	Purpose: Diagnosis of acute or asymptomatic infection Design: [1] Confirmed COVID cases (n = 111) [1a] Symptomatic cases (n = 81) [1b] Asymptomatic cases (n = 30) [2] Non‐COVID patients (suspected COVID with multiple negative PCR tests) (n = 40) Recruitment: There were 111 patients with positive RT‐PCR test results at the time of admission and 40 suspected patients from Feb 3 to Mar 13 were enrolled. The suspected cases were based on clinical manifestation, chest radiography and epidemiology. All suspected patients were eventually "excluded from diagnosis" [and used as non‐COVID controls] based on clinical judgement as well as multiple negative RT‐PCR tests. Prospective or retrospective: Retrospective Sample size: 151 (111) patients, sample size unclear (65 COVID patients had a second blood sample and 54/62 discharged patients gave blood samples again in later check‐ups) 151 (111) samples seemed to be relevant for our review. Further detail: Inclusion: [1] rt‐PCR‐positive cases admitted to Union Jiangbei Hospital, Wuhan, China, from Feb 3 to Mar 13, 2020 [2] Suspected patients that were eventually excluded from diagnosis based on clinical judgement as well as multiple negative RT‐PCR tests
Patient characteristics and setting	Setting: Hospital inpatients Location: Union Jiangbei Hospital, Wuhan, China Country: China Dates: Feb 3 to Mar 13 2020 Symptoms and severity: [1a] Symptomatic (n = 81); 17 (15.5%) severe, 42 (38.2%) common, 22 (20%) mild [1b] Asymptomatic (n = 30) Demographics: [1a] Age: Median 56 (range 23, 93) years; 48/81 (59.2%) male [1b] Age: Median 56.5 (range 20, 94) years; 22/30 (73.3%) Exposure history: Possibly all from Wuhan/Hubei province Non‐Covid group 1: [2] Suspected COVID cases with negative PCR Source: Union Jiangbei Hospital, Wuhan, China from Feb 3 to Mar 13, 2020 Characteristics: Age: Median 48.5 (range 23, 98) years; 23/40 (57.4%) male Non‐Covid group 2: NA
Index tests	Test name: "COVID‐19 IgG Detection Kits" Manufacturer: Hunan Yuanjing Biotechnology Co., Ltd. Antibody: IgM, IgG Antigen target: SARS‐CoV‐2 spike receptor‐binding domain (S‐RBD) and N spike‐protein as antigens Evaluation setting: Lab test performed in lab Test method: Magnetic Beads Chemiluminescent Immunoassay Timing of samples: [1a] First sample (n = 81): Median 7 days (range 4, 14) after symptom onset [1b] First sample (n = 30): Median 8 days (range 7, 9) after the positive RT‐PCR test detection [2] Median 9.5 (range 5, 12) day after symptom onset (n = 40) Samples used: Serum Test operator: Not stated Definition of test positivity: The test results in the sample were expressed in COI. Threshold not stated Blinding reported: no Threshold predefined: not stated
Target condition and reference standard(s)	Reference standard: real‐time RT‐PCR amplification of SARS‐CoV‐2 open reading frame 1ab (ORF1ab), nucleocapsid protein (NP) genes fragments using kits (Shanghai BioGerm Biotechnology Co., Ltd) Conditions for amplification were 50 C for 10 min, 95 C for 5 min, followed by 40 cycles of 95 C for 10 s and 55 C for 40 s. The case would be considered to be laboratory confirmed when two targets (ORF1ab, NP) tested positive using specific real‐time RT‐PCR [19]. A cycle threshold value (Ct‐value) <= 38 was defined as a positive test, and a Ct‐value of > 38 was defined as a negative test. Samples used: nasopharyngeal swab Timing of reference standard: Not stated Blinded to index test: Yes, prior index test Incorporated index test: no Definition of non‐COVID cases: real‐time RT‐PCR amplification of SARS‐CoV‐2 open reading frame 1ab (ORF1ab), nucleocapsid protein (NP) genes fragments using kits (Shanghai BioGerm Biotechnology Co., Ltd) Conditions for amplification were 50 C for 10 min, 95 C for 5 min, followed by 40 cycles of 95 C for 10 s and 55 C for 40 s. The case would be considered to be laboratory confirmed when two targets (ORF1ab, NP) tested positive using specific real‐time RT‐PCR [19]. A cycle threshold value (Ct‐value) <= 38 was defined as a positive test, and a Ct‐value of > 38 was defined as a negative test. Classed as "Non‐COVID” control based on clinical judgement as well as multiple negative RT‐PCR tests Samples used: nasopharyngeal swab Timing of reference standard: Not stated Blinded to index test: Yes, prior index test Incorporated index test: no
Flow and timing	Time interval between index and reference tests: [1a] and [2] Not stated [1b] Median 8 days (range 7, 9) after the positive RT‐PCR test detection All patients received same reference standard: yes Missing data: Not stated Uninterpretable results: Not stated Indeterminate results: Not stated Unit of analysis: Samples but only 1 sample per time split
Comparative
Notes	Funding: This study was supported by the National Key R&D Programme of China [2019YFF0216303]. Publication status: Published paper Source: Annals of Medicine Author COI: No potential conflict of interest was reported by the author(s).
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?	No
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?		High risk