Although asthma is associated with an increased risk for Crohn disease, it does not increase the risk for surgery in patients who have both conditions, according to the results of a study published in Clinical Epidemiology.
Asthma and Crohn disease are both immune-mediated diseases and share some common characteristics, including their pathogenesis and environmental and genetic risk factors.
M. Ellen Kuenzig, PhD, of the Children’s Hospital of Eastern Ontario in Ottawa, Canada, and colleagues used health administrative data from a healthcare plan in Alberta, Canada, to conduct a cohort study to assess the effect of asthma on the need for surgery in patients with Crohn disease diagnosed between 2002 and 2008. They estimated the association between asthma and intestinal resection using multivariable Cox proportional hazards regression. Smoking status was inferred with a novel method that used martingale residuals derived from a data set of 485 patients enrolled in the Alberta Inflammatory Bowel Disease Consortium who completed environmental questionnaires. This latter cohort constituted the validation sample.
A total of 2113 individuals were diagnosed with Crohn disease in the Alberta health administrative database and had at least 2 years of follow-up after 2002. Of these patients, 337 (15.9%) had asthma and 5532 (25.1%) required an intestinal resection.
Investigators did not find that intestinal resection was associated with asthma in either the health administrative data (crude hazard ratio [HR], 1.02; 95% CI, 0.81-1.29) or the validation data set (crude HR, 0.82, 95% CI, 0.45-1.50). Smoking was not associated with the risk for intestinal resection in the health administrative data (HR, 1.01; 95% CI, 0.80-1.28) or in the validation sample (HR, 1.14; 95% CI, 0.85-1.51). However, in the model in which it was imputed, smoking was associated with a higher risk for surgery (HR, 1.31; 95% CI, 1.07-1.59).
These results may have been biased by the use of a validation data set derived from patients who may have had more severe disease than the health administrative database. The investigators also were not able to determine phenotype or severity of either asthma or Crohn disease. Potential confounders in the data sets, including the presence of other immune-mediated diseases, healthcare utilization practices, and medication use may have also limited the study conclusions.
The investigators noted that the adjustment for unmeasured confounding variables, such as smoking, is feasible in gastrointestinal studies that use health administrative data. They suggested that future studies take a similar approach to prevent unmeasured confounding from biasing study results.
Kuenzig ME, Sadatsafavi M, Aviña-Zubieta JA, et al. Asthma is not associated with the need for surgery in Crohn’s disease when controlling for smoking status: a population-based cohort study. Clin Epidemiol. 2018;10:831-840.