Fassbender 2009.

Study characteristics
Patient sampling	Primary objective: to test the hypothesis that the plasma concentration of complement factor C3a (anaphylatoxin) can be used as a non‐invasive test in the diagnosis of endometriosis Participants: women who had undergone laparoscopic surgery for subfertility, pelvic pain or both Selection criteria: not specified Study design: cross‐sectional prospective single‐gate design, non‐consecutive enrolment
Patient characteristics and setting	Clinical presentation: infertility ‐ 160, dysmenorrhoea ‐ 26, hx of hormonal treatment, chronic PID or STI ‐ nil; ethnicity: Caucasian ‐ 136, other ‐ 24 Age: median (range) 30 (18–46) years (endometriosis), 33 (20–46) years (controls) Number of participants enrolled: 160 women Number of participants available for analysis: 160 women (49 in menstrual, 55 in follicular, 56 in luteal cycle phase) Setting: Leuven University Fertility Centre Place of study: Leuven, Belgium Period of study: not stated Language: English
Index tests	Index test: C3a (anaphylatoxin) Details of the index test procedure as stated: plasma concentration of C3a‐des‐Arg was determined with a commercially available immunoassay (Quidel Inc, San Diego, USA); quantification with a standard curve; sensitivity of this experiment was 34 ng/ml; sample handling and laboratory technique described in details Threshold for positive result: not reported Examiners: no information provided; unclear if were blinded to the results of reference standard Interobserver variability: Intra‐and interassay CV ranged 1.5%‐2.8% and 11%‐23%
Target condition and reference standard(s)	Target condition: endometriosis Prevalence of target condition in the sample: n = 109/160 (68%); severity: stage I‐II 54, stage III‐IV 55; controls n = 51 Reference standard: laparoscopy N = 160 (100%) + histology Description of positive case definition by reference standard test as reported: visualisation at surgery with subsequent histological confirmation; staging according to the rAFS classification Examiners: no information provided
Flow and timing	Time interval between index test and reference standard: blood was collected immediately before surgery Withdrawals: none
Comparative
Key conclusions by the authors	Our data do not confirm our hypothesis that C3a‐des‐Arg concentration in plasma can be used as a biomarker for the non‐invasive diagnosis of endometriosis, but does not rule out the possibility that that measurement of complement activation at the level of the cervix or endometrium may be useful for this purpose
Conflict of interest	Not reported; supported by the Flemish fund for scientific research (FWO) & Leuven University Council (Dienst Onderzoekscoordinatie KU Leuven, Leuven, Belgium)
Notes	For C3a there was no difference between the groups ‐ no data available for meta‐analysis
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	No
Did the study avoid inappropriate exclusions?	Yes
Was a 'two‐gate' design avoided?	Yes
		High	Low
DOMAIN 2: Index Test All tests
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
If a threshold was used, was it pre‐specified?	No
Was a cycle phase considered in interpretation of the result of index test?	Yes
		High	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?	Yes
		Low	Low
DOMAIN 4: Flow and Timing
Was there an appropriate interval between index test and reference standard?	Yes
Did all patients receive the same reference standard?	Yes
Were all patients included in the analysis?	Yes
		Low