Banaszkiewicz 2011.

Study characteristics
Patient sampling	Country Poland Study design Retrospective casenote review Setting Hospital Dates of data collection N/R Population (n) 965 Inclusion criteria Patients after radical surgery in whom prognosis following a possible second operation was good Exclusion criteria Non‐radical surgery or concomitant disease making survival of a second operation unlikely Participants included (n) 340
Patient characteristics and setting	Age range N/R Smoking status N/R Site of primary tumour Colorectal Stage of primary tumour Dukes A ‐ D Perioperative Investigations done to ensure no residual disease Endoscopic polypectomy Chemotherapy/radiotherapy? Radical Recurrences (n) 112 Site of recurrences Liver 44, Local 32, Lung 7, Disseminated 12, other 6, 2 sites 11
Index tests	CEA timing CEA 3, 6, 12 months, then once a year up to 5 years CEA technique N/R CEA threshold 5 µg/L Definition of positive N/R Which CEA value (s) used? N/R
Target condition and reference standard(s)	Follow‐up schedule Follow‐up visits at 3, 6, 12 months, then once a year up to 5 years. Follow‐up schedule included patient’s history and physical examination, measurement of CEA serum concentration and classic colonoscopy
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?	No
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?	Unclear
Is the same method and instrument used for all CEA measurements?	Unclear
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
		Unclear	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?	Unclear
Did all patients receive a reference standard?	Yes
		Low