Mach 1978.

Study characteristics
Patient sampling	Country Switzerland Study design Retrospective Setting Hospital Dates of data collection 1977 ‐ 1978 Population (n) 200 Inclusion criteria Histologically confirmed diagnosis of adenocarcinoma of colon or rectum Exclusion criteria Incomplete tumour resection Participants Included (n) 66
Patient characteristics and setting	Age range 65 Smoking status 12 patients who had CEA levels fluctuating around the normal limit of 5 ng/ml during the last 2 or 3 years without a definite rise of CEA levels and also without clinical evidence of tumour relapse. Among them were 6 heavy smokers Site of primary tumour Colorectal Stage of primary tumour Dukes ABCD Perioperative investigations done to ensure no residual disease N/R Chemotherapy/radiotherapy? 2 of the recurrences were reported to have chemo Recurrences (n) 19 Site of recurrences N/R
Index tests	CEA timing 3‐monthly CEA technique The radioimmunoassay of CEA was performed according to the method of Goldz as modified by Mach el al. The major modification was that duplicates of 1 ml of plasma (10 ml of blood was collected in tubes containing 33 mg of dry E.D.T.A. K3) instead of 5 ml of serum, were extracted in perchloric acid. The sensitivity of the test is 1 µg/L. The normal value determined in 90 nonsmoking blood bank donors, unselected for age and sex, ranged between 0 to 3.5 µg/L. Our CEA assay is similar to the Hansen method,'but our numerical values are slightly higher and should be divided by a factor of 1.5 in order to make a direct comparison. CEA threshold 5 µg/L Definition of positive 1 elevated value Which CEA value (s) used? All
Target condition and reference standard(s)	Follow up schedule N/R
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?	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?	Yes
Is there an estimation of reproducibility of the method, for example the % coefficient of variation at specific concentrations?	Yes
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?	No
		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?	No
Did all patients receive a reference standard?	Unclear
		Unclear