Domain	Yes	No	Unclear
Patient selection (describe methods of patient selection):
1. Was a consecutive or random sample enrolled?	The enrolment was consecutive or random.	The enrolment was not consecutive or random.	Insufficient information is available to answer ‘yes’ or ‘no’.
2. Was a case‐control design avoided?	This question is irrelevant because studies with case‐control design are excluded from the review.
3. Did the study avoid inappropriate exclusions?	All diabetic patients (type 1 and 2) with suspicious DPN were recruited regardless of any other characteristic. But exclusion of those with no diabetes and established diagnosis of DPN is common and will be accepted.	Diabetic patients (type 1 and 2) with some characteristics which may modify the performance of index tests were excluded, for example, those who were asymptomatic.	Insufficient information is available to answer ‘yes’ or ‘no’.
Risk of bias:	Low	High	Unclear
Could the selection of patients have introduced bias?	Both signalling question 1 and 3 are answered ‘yes’.	Either signalling question 1 or 3 is answered ‘no’.	Both signalling question 1 and 3 can not be answered ‘yes’ or ‘no’ because of insufficient information.
Concerns regarding applicability (describe included patients (prior testing, presentation, intended use of index test and setting)
Is there concern that the included patients do not match the review questions?	The study population represents an unselected sample of diabetics with suspected DPN in community or outpatient setting or inpatient setting, regardless of gender, presentation and severity.	The study population is selected by gender, presentation or severity. Or the study includes those with the established diagnosis of DPN or with treatment of DPN.	Insufficient information is available to answer ‘low’ or ‘high’.
Index test (describe the index test and how it was conducted and interpreted):
1. Were the index test results interpreted without knowledge of the results of reference standard?	The outcome assessors for the simple test(s) were not aware of the results of NCS.	The outcome assessors for the simple test(s) were aware of the results of NCS.	Insufficient information is available to answer ‘yes’ or ‘no’.
2. Where multiple index tests were compared in the study or had been repeatedly used before the study, were the results of the index test interpreted without knowledge of other index test results or the previous test results?	Simple test results were interpreted without any knowledge of other simple test results or the previous test results.	Simple test results were interpreted with knowledge of other simple test results or the previous test results .	Insufficient information is available to answer ‘yes’ or ‘no’.
3. If a threshold was used, was it pre‐specified?	The threshold used to define DPN is pre‐specified.	The threshold used to define DPN is derived from the results of the study, for example, the optimal threshold in ROC.	Insufficient information is available to answer ‘yes’ or ‘no’.
Risk of bias:	Low	High	Unclear
Could the conduct or interpretation of the index test have introduced bias?	When signalling 2 is applicable, all the signalling question are answered ‘yes’. When signalling 2 is not applicable, both question 1 and 3 are answered ‘yes’.	Any one of the signalling questions is answered ‘no’.	All the signalling questions can not be answered ‘yes’ or ‘no’ because of insufficient information.
Concerns regarding applicability
Are there concerns that the index test, its conduct, or interpretation differ from the review question?	The study met both of the following items: 1. Sufficient details are correctly described about the examination procedures of simple test(s) (thresholds, investigated sites, etc.) to permit its replication. 2. Simple tests were performed by qualified physicians in diabetes or neuropathy or other trained professionals.	The study did not meet either of the following items: 1. Sufficient details are correctly described about the examination procedures of simple test(s) (thresholds, investigated sites, etc.) to permit its replication. 2. Simple tests were performed by qualified physicians in diabetes or neuropathy or other trained professionals.	Insufficient information is available to answer ‘low’ or ‘high’.
Reference standard (describe the reference standard and how it was conducted and interpreted):
1. Was the reference standard likely to correctly classify the target condition?	The study met all of the following items: 1. Diagnostic criteria were up to the minimal diagnostic criteria of NCS we have pre‐defined. 2. Applicable variables, such as age, height and temperature, for NCS were considered. 3. NCS were performed by qualified physicians in diabetes or neuropathy or other trained professionals.	The study did not meet any one of the following items: 1. Diagnostic criteria were up to the minimal diagnostic criteria of NCS we have pre‐defined. 2. Applicable variables, like age, height and temperature, for NCS were considered. 3. NCS were performed by qualified physicians in diabetes or neuropathy or other trained professionals.	Insufficient information is available to answer ‘yes’ or ‘no’.
2. Were the reference standard results interpreted without knowledge of the results of the index test?	The outcome assessors for NCS were not aware of the results of the simple test(s).	The outcome assessors for NCS were aware of the results of the simple test(s).	Insufficient information is available to answer ‘yes’ or ‘no’.
Risk of bias:	Low	High	Unclear
Could the reference standard, its conduct, or its interpretation have introduced bias?	All the signalling question are answered ‘yes’.	Any one of the signalling questions is answered ‘no’.	All the signalling questions can not be answered ‘yes’ or ‘no’ because of insufficient information.
Concerns regarding applicability
Are there concerns that the target condition as defined by the reference standard does not match the review question?	The study met both of the following items: 1. Sufficient details are correctly described about the examination procedures of the NCS (thresholds, investigated sites, etc.) to permit its replication. 2. NCS was performed by qualified physicians in diabetes or neuropathy or other trained professionals.	The study did not meet either of the following items: 1. Sufficient details are correctly described about the examination procedures of the NCS (thresholds, investigated sites, etc.) to permit its replication. 2. NCS was performed by qualified physicians in diabetes or neuropathy or other trained professionals.	Insufficient information is available to answer ‘low’ or ‘high’.
Flow and timing (describe any patients who did not receive the index test(s) and/or reference standard or who were excluded from the 2 x 2 table (refer to flow diagram); describe the time interval and any interventions between index test(s) and reference standard:
1. Was there an appropriate interval between index test(s) and reference standard?	The time period was two months or less.	The time period was more than two months.	Insufficient information is available to answer ‘yes’ or ‘no’.
2. Did all patients receive a reference standard?	All patients receiving simple test(s) underwent NCS.	Not all patients receiving simple tests underwent NCS, including the case in which a random sample of those who were tested negative by simple test(s) underwent NCS and then analyses for sensitivity and specificity were adjusted or not.	Insufficient information is available to answer ‘yes’ or ‘no’.
3. Did patients receive the same reference standard?	The same NCS procedure was performed for the patients.	Different reference standards or different NCS procedure were performed for the patients.	Insufficient information is available to answer ‘yes’ or ‘no’.
4. Were index tests and reference standard tested in the same limbs	Simple tests and NCS were tested in the same limbs.	Body sites tested by simple tests and NCS had some differences.	Insufficient information is available to answer ‘yes’ or ‘no’.
5. Were all patients included in the analysis?	All patients recruited into the study were included in the analysis.	Not all the patients recruited into the study were included in the analysis.	Insufficient information is available to answer ‘yes’ or ‘no’.
Risk of bias:	Low	High	Unclear
Could the patient flow have introduced bias?	All signalling questions are answered ‘yes’.	Any signalling question is answered ‘no’.	All the signalling questions can not be answered ‘yes’ or ‘no’ because of insufficient information.
DPN: diabetic peripheral neuropathy; NCS: nerve conduction studies; ROC: receiver operator characteristic.