Wood 1980.

Study characteristics
Patient sampling	Country UK Study design Retrospective Setting Hospital Dates of data collection 1974 ‐ 1976 Population (n) 148 Inclusion criteria Apparently curative surgery for adenocarcinoma of the colon and rectum without evidence of metastatic disease Exclusion criteria N/R Participants Included (n) 148
Patient characteristics and setting	Age range N/R Smoking status N/R Site of primary tumour Colorectal Stage of primary tumour N/R Perioperative investigations done to ensure no residual disease N/R Chemotherapy/radiotherapy? N/R Recurrences (n) 36 Site of recurrences Local 17, local + liver 2, local + bone 2, local + metachronous primary 1, liver 8, bone 5, lung 2
Index tests	CEA timing Each follow‐up visit, 2 consecutive raised CEA triggered investigation for recurrence CEA technique CEA levels were assayed by a double antibody radioimmunoassay on unextracted serum CEA threshold 25 µg/L Definition of positive 2 consecutively elevated values Which CEA value (s) used? All
Target condition and reference standard(s)	Follow‐up schedule CEA at 3 ‐ 6 months intervals post‐operative for up to 56 months or until death. Reference standard If CEA positive then CXR, Liver scan, and bone scan. If these are negative, additional BE and/or 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?	Unclear
Did the study avoid inappropriate exclusions?	Unclear
		Unclear	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?	No
		High