Afzali 2016.

Study characteristics
Methods	Retrospective cohort. Study period: 1992 to 2012
Participants	Country: USA. UC and CD patients who underwent either urgent or elective abdominal surgery.
Interventions	1.Preoperative methotrexate (n=15) 2. Preoperative azathioprine or 6‐mercaptopurine (n= 52) 3. No preoperative methotrexate (n=165) 4. No preoperative azathioprine or 6‐mercaptopurine (n=128)
Outcomes	Wound infection, anastomotic leak, abscess, fistula and extraabdominal infection within 30 days of surgery
Notes	NOS low risk of bias overall Adjusted ORs for methotrexate and azathioprine were obtained from multivariate logistic regression model.
Risk of bias
Bias	Authors' judgement	Support for judgement
Representativeness of the exposed cohort	Low risk	All CD and UC who underwent abdominal surgery at the Univerity of Washington Medical Center from 1993 to 2012
Selection of the non exposed cohort	Low risk	Both groups obtained from the same hospital and time period
Ascertainment of exposure	Low risk	Medical records were examined
Demonstration that outcome of interest was not present at start of study	Unclear risk	No information was provided
Comparability of cohorts (Controlled for critical factor/other medications)	Low risk	Adjusted for steroid use
Comparability of cohorts (Controlled for additional factor)	Low risk	Also adjusted for albumin, hematocrit, smoking status, and BMI
Assessment of outcome	Low risk	Medical records were examined
Was follow‐up long enough for outcomes to occur	Low risk	30 days
Adequacy of follow up of cohorts	Low risk	61 patients excluded from analysis due to missing BMI measurement