Clarke 2020.

Study characteristics
Patient Sampling	Purpose: Diagnosis of current convalescent‐phase infection or prior infection Design: Single‐group study to estimate sensitivity and specificity [1] Confirmed COVID patients (n = 79) [2] Suspected COVID, PCR‐negative patients (n = 42) [3] Concurrent, untested, asymptomatic patients (n = 235) Group [3] not eligible for our review as a high‐risk group without reference standard Recruitment: Patients receiving dialysis within two units affiliated with Imperial College Renal and Transplant Centre between April 27 and May 7, 2020 who were routinely screened for the development of symptoms or a fever prior to each haemodialysis session Prospective or retrospective: Prospective Sample size: 356 (79) of which 121 (79) are eligible for our review Further detail: Inclusion: Patients receiving dialysis within two units affiliated with Imperial College Renal and Transplant Centre between April 27 and May 7, 2020 Exclusion from analysis: No informed consent
Patient characteristics and setting	Setting: Seroprevalence screening Location: Imperial College Renal and Transplant Centre, London, UK Country: UK Dates: April 27 and May 7, 2020 Symptoms and severity: All symptomatic Demographics: Patients with end‐stage kidney disease receiving haemodialysis (n = 79) Age: Median 65 (range 54–73) years Sex: 26 (32.9%) women Ethnicity: Black 9 (11.4%) White 19 (24.1%) Indoasian 38 (48.1%) Other 13 (16.5%) Immunosuppressed 8 (10.1%) Exposure history: Exposure within dialysis units Non‐Covid group 1: [2] Suspected COVID, PCR‐negative Source: Imperial College Renal and Transplant Centre, London, UK between April 27 and May 7, 2020 Characteristics: Patients with end‐stage kidney disease receiving haemodialysis with COVID symptoms (n = 42) Age: Median 62 (range 51–74) years Sex: 20 (47.6%) women Ethnicity: Black 8 (19.0%) White 9 (21.4%) Indoasian 19 (45.2%) Other 6 (14.2%) Immunosuppressed 4 (9.5%) Exposure within dialysis units Non‐Covid group 2: [3] Concurrent asymptomatic (untested) Source: Imperial College Renal and Transplant Centre, London, UK between April 27 and May 7, 2020 Characteristics: Patients with end‐stage kidney disease receiving haemodialysis without COVID symptoms (n = 235) Age: Median 68 (range 54–73) years Sex: 84 (35.7%) women Ethnicity: Black 29 (12.3%) White 62 (26.4%) Indoasian 97 (41.2%) Other 47 (20.0%) Immunosuppressed 43 (18.3%) Exposure within dialysis units
Index tests	Test name: [A] Abbott SARS‐CoV‐2 IgG assay Manufacturer: [A] Abbott Antibody: IgG Antigen target: Nucleocapsid‐protein antigen Evaluation setting: Lab test performed in lab Test method: Automated (Architect system) two‐step chemiluminescent microparticle immunoassay (CLIA) Timing of samples: [1] Mean 34+/‐6.4 days, median 22 (range 14–34) days after PCR testing [2] Median time between tests was 23 (14–35) days [3] Asymptomatic Samples used: Serum Test operator: Staff working in the Department of Infection and Immunity, North West London Pathology NHS Trust. Definition of test positivity: The index (sample/control) is calculated by comparing relative light units in the sample to the calibrator relative light units. Samples were interpreted as positive or negative according to the manufacturer’s instructions, with a cut‐off index value of 1.4. Blinding reported: Not stated Threshold predefined: yes, according to the manufacturer's instructions (S/C index)
Target condition and reference standard(s)	Reference standard: Routine screening of patients for the development of symptoms or a fever occurred prior to each haemodialysis session from March 9. Symptomatic patients received real‐time RT‐PCR assay of nasopharyngeal swab specimens following either routine screening or acute presentation; RT‐PCR was carried out as per PHE guidelines using certification marked assays with primers directed to the nucleocapsid or RNA‐dependent RNA polymerase genes. Threshold not stated Samples used: nasopharyngeal swab specimens Timing of reference standard: Not stated Blinded to index test: yes, prior Incorporated index test: no Definition of non‐COVID cases: [2] Routine screening of patients for the development of symptoms or a fever occurred prior to each haemodialysis session from March 9. Real‐time RT‐PCR assay of nasopharyngeal swab specimens following either routine screening or acute presentation; RT‐PCR was carried out as per PHE guidelines using certification marked assays with primers directed to the nucleocapsid or RNA‐dependent RNA polymerase genes. Threshold not stated [3] Routine screening of patients for the development of symptoms or a fever occurred prior to each haemodialysis session from March 9 (no PCR test) Samples used: [2] nasopharyngeal swab specimens [3] None Timing of reference standard: [2] Not stated [3] No reference standard as no symptoms Blinded to index test: yes, prior Incorporated index test: no
Flow and timing	Time interval between index and reference tests: [1] Mean 34+/‐6.4 days, median 22 (range 14–34) days after PCR testing [2] Median time between tests was 23 (14–35) days [3] No reference standard All patients received same reference standard: yes for [1] and [2]; no reference standard for [3] Missing data: Exclusion of 235 PCR‐untested patients (group [3]) Uninterpretable results: None Indeterminate results: 3 of 356 (0.84%) patients had a borderline antibody result that was within +/‐20% of the cut‐off index for a positive result. Unit of analysis: Patients
Comparative
Notes	Funding: This research is supported by the National Institute for Health Research (NIHR) Imperial Biomedical Research Centre based at Imperial College Healthcare NHS Trust and Imperial College London. Publication status: Published paper (rapid communication) Source: Journal of the American Society of Nephrology (JASN) Author COI: Dr. Liz Lightstone reported grants from Roche, outside the submitted work. M. Griffith reported an educational grant from Vifor Pharmaceuticals for £400 to attend the American Society of Nephrology 2019, outside the submitted work.
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?	Yes
Did the study avoid inappropriate exclusions?	Yes
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?			Low concern
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	No
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?		High 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?	Yes
Could the patient flow have introduced bias?		High risk