Li Destri 1998.

Study characteristics
Patient sampling	Country Italy Study design Retrospective Setting Hospital Dates of data collection N/R Population (n) 364 Inclusion criteria Radical surgery for colorectal cancer CEA measured postoperatively Exclusion criteria N/R Participants included (n) 239
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? No Recurrences (n) 45 Site of recurrences hepatic 18, non‐hepatic 22, mixed 5
Index tests	CEA timing CEA monitoring, conducted every 3 months for years 1, 2, and 3, every 6 months for years 4 and 5, then yearly up to year 10 CEA technique The antigen was determined using the radioimmunoassay method. 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 CEA monitoring, conducted every 3 months for years 1, 2, and 3, every 6 months for years 4 and 5, then yearly up to year 10.
Flow and timing	Timing of CEA vs reference standard (days) N/R
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?	Unclear
Were the reference standard results interpreted without knowledge of the results of the index tests?	Unclear
		Unclear	Unclear
DOMAIN 4: Flow and Timing
Did all patients receive the same reference standard?	Unclear
Were all patients included in the analysis?	Yes
Was the index test repeated prior to the reference standard?	Unclear
Was the the timing between index test(s) and reference standard ascertainable?	Unclear
Did all patients receive a reference standard?	Unclear
		Unclear