Nasir 2010.

Study characteristics
Methods	Retrospective cohort. Study period: 2005 to 2009
Participants	Country: USA. CD patients who underwent operations resulting in an anastomosis. Emergency surgeries and proximal diversions were excluded
Interventions	1. Preoperative anti‐TNF therapy (n= 119) within 8 weeks of surgery 2. No preoperative anti‐TNF therapy (n= 251)
Outcomes	Intraabdominal abscess and anastomotic leak 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 operations resulting in an anastomosis from 2005 to 2009
Selection of the non exposed cohort	Low risk	Both groups obtained from the same hospital database and time period
Ascertainment of exposure	Low risk	Data obtained from prospectively maintained 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	Did not control for other medications
Comparability of cohorts (Controlled for additional factor)	High risk	Did not control for additional factors
Assessment of outcome	Low risk	Data obtained from prospectively maintained database
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Unclear risk	Information not provided