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. 2018 Sep 24;9(9):188. doi: 10.1038/s41424-018-0054-z

Table 1.

Characteristics of included studies

Study Country Study design Data source (years of study) Definition of IBD Definition of asthma Relative timing of diagnoses Type of IBD Matched variables and covariates Age of participants Sample size
Bernstein23 Canada Matched case-control Provincial health administrative data (1984–2003) Validated algorithm ≥5 health care contacts for asthma Asthma diagnosed before or after IBD CD, UC Matched on age, sex, and rural/urban residence Pediatric and adult IBD: 8072 Controls: 80,489
Boneberger52 Chile Case-control Tertiary-care center (2009–2010) Routine clinical practice Not specified Not specified UC Adjusted for age and sex Range: 6 to 45 years at study entry IBD: 52 Controls: 174
Brassard42 Canada Retrospective cohort Provincial health administrative data (2001–2006) Externally validated algorithm ≥3 prescriptions for respiratory medication within 1 year, on at least two separate occasions; the third prescription must have occurred at ≤40 years of age Asthma diagnosed before IBD CD, UC Incidence rates were standardized based on age and sex ≤40 years at asthma diagnosis Asthma: 136,178a
D’Arienzo50 Italy Case-control Tertiary-care center (1998) Standard diagnostic criteria Standard diagnostic criteria Not specified UC None Range: 16 to 69 years IBD: 50 Controls: 50
D’Arienzo51 Italy Matched case-control Tertiary-care center (2000) Standard diagnostic criteria Standard diagnostic criteria Not specified UC Matched controls were partners of cases Adult IBD: 45 Controls: 37
Gearry24 New Zealand Frequency matched case-control Canterbury IBD Study (2003–2005) Standard diagnostic criteria Not specified Not specified CD, UC Frequency matched based on age (at recruitment) and sex. Adjusts for family history of IBD, smoking status, age, social class at birth, sex, and ethnicity Adult IBD: 1291 Controls: 600
Hammer43 United Kingdom Matched case-control Tertiary-care center (1952–1965) Standard diagnostic criteria Questionnaire or interview Not specified Colonic CD, UC None Not specified IBD: 243 Controls: 319
Hemminki28 Sweden Prospective cohort National health administrative data (1964–2007) Hospitalization with an ICD code for IBD Hospitalization with an ICD code for asthma IBD diagnosed after asthma CD, UC Standardized incidence rates used expected number of cases based on age, sex, year, region, and socioeconomic status Children and adults Asthma: 148,295c
Kappelman44 United States Matched case-control PharMetrics Patient-Centric Database (2003–2004) Validated algorithm ICD code for asthma Not specified CD, UC Matched on age, sex, health plan type, and geographic region Children only IBD: 1242 Controls: 3353
Kuenzig22 Canada Case-control Population-based health administrative data (1994–2010) Validated algorithm Externally validated algorithm 1. Asthma before IBD
2. Asthma diagnosed before or after IBD		 CD, UC Age, sex, rural/urban residence, socioeconomic status Children and adults IBD: 5464 Controls: 402,800
Livnat45 Israel Case-control Tertiary-care center (2008–2009b) Standard diagnostic criteria Self-report Not specified CD None Children and young adults IBD: 23 Controls: 24
Myrelid46 Sweden Matched case-control Cases: Unclear controls: Southeastern Region Population Registry (2000) Standard diagnostic criteria Self-report Not specified CD Age, gender, place of residence, and other atopic manifestations (allergic rhinitis, eczema) Range: 18 to 50 years IBD: 275 Controls: 777
Nakamura30 Japan Matched case-control Cases: Patients receiving financial aid from the Japanese government for the treatment of UC (1988–1990) Controls: Patients on the roster of a health check-up program Diagnosis of UC by treating physician, and confirmation of diagnosis by independent group for approval of financial aid Self-report questionnaire Asthma before IBD UC Matched on age and sex Children and adults IBD: 384 Controls: 384
Neilly47 Scotland Matched case-control Not specified Not specified Previous physician-diagnosed asthma and/or history of persistent or episodic wheeze with breathlessness, responsive to bronchodilator therapy Not specified CD Matched on age, sex, and smoking history Adults IBD: 29 Controls: 29
Peng29 Taiwan Frequency matched retrospective cohort National health administrative data (2000–2011) ICD codes for IBD ICD code for asthma and treated with inhaled corticosteroids, systemic corticosteroids, or inhaled short-acting ß2 agonists Asthma diagnosed after IBD CD, UC Frequency matched on age, sex, and index year. Adjusted for age, sex, and other comorbidities (rhinitis, chronic sinusitis, atopic dermatitis, and chronic obstructive pulmonary disease) Adults IBD: 319 Controls: 807
Pugh48 UK Matched case-control Tertiary care center; Ileostomy Association Standard diagnostic criteria Self-report Not specified CD, UC Some controls were partners of cases. Others were matched to cases based on age and sex Not specified IBD: 500 Controls: 500
Raj49 UK Cohort Tertiary-care center (1995–2005) Standard diagnostic criteria Consistent clinical picture with objective evidence of variable outflow obstruction and/or airway hyper-responsiveness IBD preceded the onset of respiratory disease in all cases but 1 CD, UC None Mean age:
• UC: 61
• CD: 60		 Asthma: 893a
Virta26 Finland Matched case-control National health administrative data (1994–2010) Received special reimbursement for IBD Received special reimbursement for asthma Asthma diagnosed before IBD CD, UC Matched on date of birth, sex, and place of residence Pediatric IBD: 595 Controls: 2380
Weng27 United States Matched case-control Kaiser Permanente Medical Care Program (1996–2005) ≥2 inpatient or outpatient ICD codes for IBD ≥2 inpatient or outpatient ICD codes for asthma Asthma could be diagnosed either before or after the diagnosis with IBD CD, UC, IBD-U Matched on age, sex, and length of enrolment in health maintenance organization. Adjusted for smoking. Children and adults IBD: 12,601 Controls: 50,404

CD Crohn’s disease, IBD inflammatory bowel disease, IBD-U inflammatory bowel disease type unclassified, ICD International Classification of Diseases, UC ulcerative colitis

aThe risk of IBD in patients with asthma was compared to the previously reported risk of IBD in the general population

bYears of study obtained from study protocol on clinicaltrials.gov

cThe risk of IBD in patients with asthma was compared to the number of cases that would be expected if there was no association between asthma and IBD