Norgard 2013.

Study characteristics
Methods	Retrospective cohort. Study period: 2003 to 2010
Participants	Country: Denmark. CD patients who underwent abdominal surgery in the Danish National Patient Registry
Interventions	1. Preoperative anti‐TNF therapy (n= 214) within 12 weeks 2. No preoperative anti‐TNF therapy (n= 2079)
Outcomes	Anastomotic leak, intraabdominal abscess, bacteremia within 30 days of surgery
Notes	NOS very high risk of bias overall
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	CD patients who underwent abdominal surgery from 2003 to 2010
Selection of the non exposed cohort	Low risk	Both groups obtained from the same database and time period
Ascertainment of exposure	Low risk	Exposure identified by codes from the National Patient Registry and prescription database
Demonstration that outcome of interest was not present at start of study	Unclear risk	Information not provided
Comparability of cohorts (Controlled for critical factor/other medications)	High risk	OR adjusted for age, gender, comorbidity, steroids, duration of CD, year and length of inpatient stay was available for anastomotic leak and intraabodminal abscess outcomes separately. Combined event rate of anastomotic leak and intraabdominal abscess was used for our analysis.
Comparability of cohorts (Controlled for additional factor)	High risk	See above
Assessment of outcome	Low risk	Outcome identified by codes from the National Patient Registry
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Low risk	All patients had 30 and 60 day follow up data after surgery