Beart 1981.

Study characteristics
Patient sampling	Country USA Study Design Prospective Setting Department of Surgery and Oncology, Mayo Clinic and Mayo Foundation Dates of data collection 1976 ‐ 1986 Population (n) 149 Inclusion criteria Resection of Dukes' B2 or C colorectal carcinoma was followed from the time of operation until the time of tumour recurrence or writing the published paper Exclusion criteria N/R Participants included (n) 149
Patient characteristics and setting	Age range N/R Smoking status N/R Site of primary tumour Colon Stage of primary tumour Dukes B or C Perioperative investigations done to ensure no residual disease N/R Chemotherapy/radiotherapy? Some got radiotherapy, chemotherapy, and/or immunotherapy. Numbers not specified Recurrences (n) 34 Site of recurrences Liver metastasis 14, Chest 6, Pelvic disease 12
Index tests	CEA Timing At least every 15 week 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 At least every 15 weeks a complete history was taken and physical examination was carried out. A CXR was obtained, and laboratory determinations included complete blood count, alkaline phosphatase, SGOT, SGPT, and CEA. LDH and proctoscopic examinations were done every 6 months. A BE and liver scanning were done annually Reference standard Additional tests including CT, laparoscopy, liver biopsy, and abdominal exploration were ordered as indicated by the history, physical examination, or positive laboratory results. All recurrent tumours were documented histologically
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?	Yes
		Low	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?	No
Were all patients included in the analysis?	No
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
		High