Lucha 1997.

Study characteristics
Patient sampling	Country USA Study design Retrospective Setting Hospital Dates of data collection 1981 ‐ 1985 Population (n) N/R Inclusion criteria Newly diagnosed colorectal cancer undergoing operative resection for cure (Astler Coller A,B,C) Exclusion criteria Metastatic disease and synchronous cancers Participants Included (n) 285
Patient characteristics and setting	Age range 66.8 (range, 31 ‐ 96) Smoking status N/R Site of primary tumour Colorectal Stage of primary tumour Astler‐Coller Stage A 39, B1 57, B2 109, C1 15, C2 60 Perioperative investigations done to ensure no residual disease Intraoperative criteria for curative resection included absence of gross residual disease Chemotherapy/radiotherapy? No Recurrences (n) 66 Site of recurrences N/R
Index tests	CEA timing 2‐monthly for 2 years, 3‐monthly for year 3, 6‐monthly for years 4 ‐ 5, annually afterwards. A repeat CEA was performed in patients who had an abnormal rise CEA technique Abbott CEA threshold 5 µg/L Definition of positive 2 consecutive samples Which CEA value (s) used? At time of recurrence
Target condition and reference standard(s)	Follow‐up schedule 2 monthly for 2 years, 3 monthly for year 3, 6 monthly for years 4 and 5, annually afterwards. A detailed history and physical examination was performed, and CEA levels were monitored at each encounter. Reference standard Two successive CEA elevations were investigated with diagnostic imaging and / or endoscopy when indicated.
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?	Yes
Did the study avoid inappropriate exclusions?	Yes
		Low	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	Unclear
DOMAIN 4: Flow and Timing
Did all patients receive the same reference standard?	No
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?	Yes
Did all patients receive a reference standard?	No
		High