1. Application of the QUADAS‐2 tool for assessing methodological quality of included studies.

Domain	Signalling question	Signalling question	Signalling question	Risk of bias	Concerns for applicability
Domain 1: Participant sampling
Participant sampling	Was a consecutive or random sample of participants enrolled?	Was a case‐control design avoided?	Did the study avoid inappropriate exclusions?	Could the selection of participants have introduced bias?	Are there concerns that the included participants and setting did not match the review question?
	Yes: all consecutive participants or random sample of participants with suspected common bile duct stones were enrolled. No: selected participants were enrolled. Unclear: this was not clear from the report.	Yes: case‐control design was avoided. No: case‐control design was not avoided. Unclear: this was not clear from the report.	Yes: the study avoided inappropriate exclusions (i.e., people who were difficult to diagnose). No: the study excluded participants inappropriately. Unclear: this was not clear from the report.	Low risk: 'yes' for all signalling questions. High risk: 'no' or 'unclear' for at least 1 signalling question.	Low concern: the selected participants represented the people in whom the tests would be used in clinical practice (see diagnostic pathway (Figure 1). High concern: there was high concern that participant selection was performed in a such a way that the included participants did not represent the people in whom the tests would be used in clinical practice.
Domain 2: Index test
Index test(s)	Were the index test results interpreted without knowledge of the results of the reference standard?	If a threshold was used, was it pre‐specified?	‐	Could the conduct or interpretation of the index test have introduced bias?	Were there concerns that the index test, its conduct, or interpretation differed from the review question?
	Yes: index test results were interpreted without knowledge of the results of the reference standard. No: index test results were interpreted with knowledge of the results of the reference standard. Unclear: this was not clear from the report.	Yes: if the criteria for a positive test result were pre‐specified. No: if the criteria for a positive test result were not pre‐specified. Unclear: this was not clear from the report.	‐	Low risk: 'yes' for all signalling questions. High risk: 'no' or 'unclear' for at least 1 of the 2 signalling questions.	High concern: there was high concern that the conduct or interpretation of the index test differed from the way it was likely to be used in clinical practice. Low concern: there was low concern that the conduct or interpretation of the index test differed from the way it was likely to be used in clinical practice.
Domain 3: Reference standard
Target condition and reference standard(s)	Was the reference standard likely to correctly classify the target condition?	Were the reference standard results interpreted without knowledge of the results of the index tests?	‐	Could the reference standard, its conduct, or its interpretation have introduced bias?	Are there concerns that the target condition as defined by the reference standard did not match the review question?
	Yes: all participants underwent the acceptable reference standard. No: if all participants did not undergo an acceptable reference standard. Such studies were excluded from the review. Unclear: if the reference standard that the participants underwent was not stated. Such studies were excluded from the review.	Yes: reference standard results were interpreted without knowledge of the results of the index test. No: reference standard results were interpreted with the knowledge of the results of the index test. Unclear: this was not clear from the report.	‐	Low risk: 'yes' for all signalling questions. High risk: 'no' or 'unclear' for at least 1 of the 2 signalling questions.	Low concern: participants underwent endoscopic or surgical exploration for common bile duct stone. High concern: no participants underwent endoscopic or surgical exploration for common bile duct stone.
Domain 4: Flow and timing
Flow and timing	Was there an appropriate interval between index test and reference standard?	Did all participants receive the same reference standard?	Were all participants included in the analysis?	Could the participant flow have introduced bias?	‐
	Yes: the interval between index test and reference standard was shorter ≤ 4 weeks (arbitrary choice). No: the interval between index test and reference standard was > 4 weeks. Unclear: this was not clear from the report.	Yes: all participants underwent endoscopic or surgical exploration for common bile duct stone irrespective of the index test results. No: participants underwent endoscopic or surgical exploration if the index test results were positive and underwent clinical follow‐up for at least 6 months if the index test results were negative. Unclear: this was not clear from the report. Such studies were excluded.	Yes: all participants meeting the selection criteria (selected participants) were included in the analysis, or data on all the selected participants were available so that a 2 x 2 table including all selected participants could be constructed. No: not all participants meeting the selection criteria were included in the analysis or the 2 x 2 table could not be constructed using data on all selected participants. Unclear: this was not clear from the report.	Low risk: 'yes' for all signalling questions. High risk: 'no' or 'unclear' for at least 1 signalling question.	‐