Hogan 2020a [A].

Study characteristics
Patient Sampling	Purpose: Diagnosis of current acute‐phase infection or current convalescent‐phase infection Design: Two‐group study to estimate sensitivity and specificity [1] Confirmed COVID cases (51 samples) [2] Non‐COVID samples (62 samples), current PCR‐ Recruitment: Between April 15 and June 1, 2020, residual serum samples ordered for routine medical management of inpatients at the University of Kansas Hospital Samples were collected for two groups: [1] serum samples from patients who tested positive for SARS‐CoV‐2 by an RT‐PCR assay; [2] serum samples from randomly selected patients who had tested negative for SARS‐CoV‐2 by an RT‐PCR assay within 48 hours prior to collection. All available serum samples from PCR‐positive patients and randomly selected PCR‐negative patients that were older than 18 years with adequate residual volume for parallel testing were included. Prospective or retrospective: Retrospective Sample size: 113 (51) of which 79 (17) were eligible for our review. Further detail: [1] Hospital inpatients who tested positive for SARS‐CoV‐2 by an RT‐PCR assay, [2] Hospital inpatients who had tested negative for SARS‐CoV‐2 by an RT‐PCR assay within 48 hours prior to collection. [1] and [2] older than 18 years with adequate residual volume for parallel testing
Patient characteristics and setting	Setting: Hospital inpatients Location: University of Kansas Hospital, Kansas City Country: Kansas, USA Dates: Between April 15 and June 1, 2020 Symptoms and severity: Not stated (all hospitalised, likely "greater average patient acuity") Demographics: 0‐6 days post‐PCR+ (n = 17); 71% (12/17) female; median age 71 (IQR 52‐77) years 7‐13 days post‐PCR+ (n = 17); 53% (9/17) female; median age 64 (IQR 42‐74) years 14+ days post‐PCR+ (n = 17); 53% (9/17) female; median age 64 (IQR 55‐69) years Exposure history: Not stated Non‐Covid group 1: [2] Current non‐COVID patients with other diseases Source: University of Kansas Hospital, Kansas City, Kansas (USA) between April 15 and June 1, 2020 Characteristics: Hospital inpatients, adults: 63% (39/62) female; median 53 (IQR 35‐70) years; patient samples representative of the current local circulating viruses among individuals with healthcare contacts
Index tests	Test name: [A] Liaison SARS‐CoV‐2 S1/S2 IgG [B] Elecsys anti‐SARS CoV‐2 total antibody [C] Access SARS‐CoV‐2 IgG Manufacturer: [A] DiaSorin S.p.A., Saluggia, Italy [B] Roche Diagnostics, Rotkreuz, Switzerland [C] Beckman Coulter, Inc., Minnesota, USA Antibody: [A] IgG [B] Total antibodies [C] IgG Antigen target: [A] S1 and S2 subunits of the spike‐protein [B] N‐protein [C] receptor binding domain (RBD) of the S1‐protein Evaluation setting: Lab tests performed in lab Test method: [A] indirect CLIA [B] ECLIA [C] CLIA Timing of samples: 1‐45 days overall (median: 9) post‐PCR+: 0‐6 days (median 5) post‐PCR+: 17/51 7‐13 days (median 9) post‐PCR+: 17/51 14+ days (median 18) post‐PCR+: 17/51 Combined samples were represented by the day farthest from the patient’s positive PCR test. Samples used: Residual serum samples were centrifuged, aliquoted, and frozen at ‐30 °C for 1 to 46 days. Samples were sequentially thawed and maintained at 2‐8 °C for < 14 days prior to testing. Test operator: Clinical Laboratory Scientists Definition of test positivity: [A] Reported in arbitrary units per millilitre (AU/mL). A result of < 15 was considered negative while a result of ≥ 15.0 was considered positive. [B] Results were expressed as a cut‐off index (COI). A result of < 1.0 was considered non‐reactive while a result of ≥ 1.0 was considered reactive. [C] The light signal was compared to the cut‐off value and was expressed as a signal to cut‐off ratio (S/CO). A result of < 0.8 was interpreted as non‐reactive while a result of ≥ 1.0 was considered reactive. Results between 0.8 and 1.0 (inclusive) were considered equivocal. For the purposes of analysis, equivocal results were treated as negative. Blinding reported: No, clinical Laboratory Scientists were not specifically blinded to the clinical status or PCR results of the patients. Threshold predefined: [A], [B], [C] yes, according to manufacturer's instructions
Target condition and reference standard(s)	Reference standard: FDA EUA RT‐PCR assay (Abbott RealTime SARS‐CoV‐2 assay (Abbott Diagnostics Inc, Scarborough, ME), performed on the Abbott m2000 instrument, or the Simplex COVID‐19 Direct assay (DiaSorin Molecular LLC, Cypress CA), following manufacturer’s instructions Samples used: Nasopharyngeal swabs collected in either UTM or PBS Timing of reference standard: Not stated Blinded to index test: yes, prior index test Incorporated index test: no Definition of non‐COVID cases: FDA EUA RT‐PCR assay (Abbott RealTime SARS‐CoV‐2 assay (Abbott Diagnostics Inc, Scarborough, ME), performed on the Abbott m2000 instrument, or the Simplex COVID‐19 Direct assay (DiaSorin Molecular LLC, Cypress CA), following manufacturer’s instructions) Samples used: Nasopharyngeal swabs collected in either UTM or PBS 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: [1] 1‐45 days overall (median: 9) post‐PCR+: 0‐6 days (median 5) post‐PCR+: 17/51 7‐13 days (median 9) post‐PCR+: 17/51 14+ days (median 18) post‐PCR+: 17/51 Combined samples were represented by the day farthest from the patient’s positive PCR test. All patients received same reference standard: yes Missing data: Not stated Uninterpretable results: Not stated Indeterminate results: [C] For the purposes of analysis, equivocal results were treated as negative. 1 equivocal result for 0‐6 days post‐PCR+ Unit of analysis: Each sample represented a unique patient.
Comparative
Notes	Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not‐for‐profit sectors. Publication status: Pre‐print (not peer‐reviewed) Source: medRxiv preprint Author COI: None declared.
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?	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?			Low concern
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	Unclear
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?		Unclear 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