Carlsson 1983.

Study characteristics
Patient sampling	Country Sweden Study design Prospective study Setting Hospital Dates of data collection N/R Population (n) 163 Inclusion Criteria Curative operation for colorectal cancer Exclusion Criteria Advanced age, moving away, death 3 months postop Participants Included (n) 139
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) 50 Site of recurrences N/R
Index tests	CEA timing Blood tests 3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 42, 48, 60 months post‐1977‐ blood tests 3, 6, 12, 18, 24, 30, 36, 42, 48, 60 months CEA technique Direct radio immunoassay method developed at the Department of Nuclear Medicine, Malmo General Hospital CEA threshold 3 µg/L Definition of positive 1 elevated value Which CEA value (s) used? At time of recurrence
Target condition and reference standard(s)	Follow‐up schedule Until 1977: Follow‐up exam and rectoscopy 3, 6, 9, 12, 15, 18 ,21, 24, 26, 42, 48, 60 months. Double contrast enema 3, 12, 24, 36, 48, 60 months. CXR and blood tests 3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 42, 48, 60 months. From 1977: Physical exam and rectoscopy 3, 12, 24, 36, 48, 60 months. Double contrast enema 3, 12, 24, 36, 48, 60 months. CXR and blood tests 3, 6, 12, 18, 24, 30, 36, 42, 48, 60 months
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?	No
		High	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?	Yes
Did all patients receive a reference standard?	Yes
		Low