Caturegli 2020.

Study characteristics
Patient Sampling	Purpose: Assessment of clinical performance of COVID‐19 diagnostic test Design: Multi‐group study estimating both sensitivity and specificity Group [1] and [2] were hospitalised adults investigated for COVID‐19 selected from a cohort of patients with at least one NAT result (n = 11,066) and with available residual serum samples (n = NR): [1] COVID‐19 cases, including PCR‐confirmed (n = 50, including 38 with single positive result) and clinically defined PCR‐negative based on medical record review (n = 10) [2]: Symptomatic patients with negative PCR (n = 55, including 43 with single negative result) [3] Laboratory controls including healthy lab employees and patients with polyclonal activation of antibody response (n = 513; 325 pre‐pandemic and 188 contemporaneous) Recruitment: Convenience Prospective or retrospective: Retrospective Sample size: Hospitalised COVID suspects: 115 (60) Full sample: 628 (60)
Patient characteristics and setting	Setting: Mixed Groups [1] and [2]: Inpatient service of a tertiary hospital Group [3] healthy and patients Location: Johns Hopkins Hospital, Baltimore, MD Country: United States Dates: 11 Mar to 12 Apr, 2020 Symptoms and severity: Group [1]: All symptomatic individuals. No clear details on severity but likely moderate to critical because they were all hospitalised and some developed ARDS. Demographics: Age, median (IQR): 59 (48‐70) Sex: 43/60 (72%) male Exposure history: 21/60 (35%) had travel history 20/60 (33%) had sick contacts 5/60 (8%) were healthcare workers Non‐Covid group 1: Group [2]: Symptomatic patients with negative PCR Source: Hospitalised patients who underwent one or more PCR tests for SARS‐CoV‐2 between 11 Mar and 12 Apr, 2020 Characteristics: Age, median (IQR): 61 (47‐69) Sex: 22/60 (40%) male All symptomatic, with fever (31%), cough (55%), shortness of breath (47%) the most common symptoms Non‐Covid group 2: Group [3]: non‐COVID controls (pre‐pandemic and contemporaneous) Source: Lab stocked samples mostly collected during the pre‐pandemic period (n = 327), except for 188 samples that were obtained in 2020.
Index tests	Test name: Anti‐SARS‐CoV‐2 ELISA IgG and IgA Manufacturer: EUROIMMUN AG Antibody: IgG, IgA Antigen target: S1 domain of the spike‐protein Evaluation setting: Lab tests, done in lab Test method: Enzyme‐linked immunosorbent assay (ELISA) Timing of samples: Multiple samples taken from each patient at various points in time, from 0 to 59 days after symptom onset Samples used: Residual serum samples Test operator: Not stated Definition of test positivity: positive if ratio > 1.1 Also reported threshold derived based on collected data (not extracted) Blinding reported: Unclear Threshold predefined: Yes, as per manufacturer
Target condition and reference standard(s)	Reference standard: RT‐PCR test (no further details available ‐ unclear whether more than one assay was used to test patients) AND clinical evaluation based on clinical record review (risk factors, signs and symptoms on presentation, radiologic findings, comorbidities, smoking and alcohol history, BMI, reason for repeated NAAT testing (as applicable), and complications during hospital stay. No formalised combination of findings to indicate COVID‐19 was reported. Samples used: Nasopharyngeal swabs Timing of reference standard: Not stated; duration of symptoms on clinical presentation was 7 days (range 4 to 7) for cases and 3 days (range 1 to 7) for non‐COVID patients Blinded to index test: For PCR, yes but record review was post hoc Incorporated index test: No Definition of non‐COVID cases: Group [2]: RT‐PCR (as above) Group [3]: pre‐pandemic and contemporaneous (no testing) Samples used: Group [2]: Nasopharyngeal swab Group [3]: NA Timing of reference standard: Group [2]: Not stated Group [3]: NA Blinded to index test: Group [2]: Yes (done earlier) Group [3]: NA Incorporated index test: No
Flow and timing	Time interval between index and reference tests: Not stated. Only time from symptom onset for index test was available. All patients received same reference standard: No Missing data: None reported Uninterpretable results: None reported Indeterminate results: None reported Unit of analysis: Samples
Comparative
Notes	Funding: The study was funded internally by the Clinical Immunology Laboratory of the Department of Pathology, Johns Hopkins Hospital. Publication status: Published article Source: Academic journal 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?	No
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?			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?	Unclear
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?			Unclear
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?	No
Could the patient flow have introduced bias?		High risk