Kim 2013.

Study characteristics
Patient sampling	Country Korea Study design Retrospective Setting Hospital Dates of data collection 2005 ‐ 2009 Population (n) N/R Inclusion criteria Radical resection Exclusion criteria Patients with stage 0, I or IV cancer, insufficient follow‐up (less than 3 years), abnormal CEA in the first measurement after surgery (checked within three months after surgery), history of other cancers and/or history of preoperative concurrent chemoradiation therapy were excluded Participants Included (n) 336
Patient characteristics and setting	Age range Stage 111: 29 ‐ 81, Stage 11: 33 ‐ 83 Smoking status N/R Site of primary tumour Colorectal Stage of primary tumour Stage II 189, Stage III 147 Perioperative investigations done to ensure no residual disease N/R Chemotherapy/radiotherapy? N/R Recurrences (n) 79 Site of recurrences
Index tests	CEA timing CEA levels were assayed with a 3‐month interval for the first 2 years and every 6 months thereafter CEA technique Immunoassay method (ADIVA Centaur XP immunoassay system, Siemen AG, Erlangen, Germany) CEA threshold 5 µg/L Definition of positive 1 elevated value Which CEA value (s) used? All
Target condition and reference standard(s)	Follow‐up schedule CEA levels were assayed with a 3‐month interval for the first 2 years and every 6 months thereafter. Chest CT and abdomino‐pelvic CT were performed with a 6‐month interval for the first 2 years and every year thereafter Reference standard The diagnosis of a tumour recurrence was confirmed by biopsy and radiologic evidence
Flow and timing	Timing of CEA vs reference standard (days) per protocol
Comparative
Notes
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Unclear
Did the study avoid inappropriate exclusions?	No
		High	Low
DOMAIN 2: Index Test All CEA thresholds
If a threshold was used, was it pre‐specified?	Yes
Is the same method and instrument used for all CEA measurements?	Yes
Is there an estimation of reproducibility of the method, for example the % coefficient of variation at specific concentrations?	No
Is there an indication of method accuracy, for example, is there evidence of participation in an external quality assessment and proficiency testing scheme?	No
		Low	Low
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	No
		Low	Low
DOMAIN 4: Flow and Timing
Did all patients receive the same reference standard?	Yes
Were all patients included in the analysis?	Yes
Was the index test repeated prior to the reference standard?	No
Was the the timing between index test(s) and reference standard ascertainable?	No
Did all patients receive a reference standard?	Yes
		Low