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