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How Diabetes Increases Asthma Exacerbations

Oct 22, 2019
 
Editor: Steve Freed, R.PH., CDE

Author: Nour Salhab, Pharm.D. Candidate, USF College of Pharmacy

Obesity and uncontrolled blood glucose have effects on asthma exacerbations.

Metabolic dysfunction is one of the hypotheses that was linked to obese asthma. If not properly treated, obese asthma can lead to morbidity. Existing studies, which are mainly cross-sectional, cannot fully determine the connection between metabolic conditions and asthma. Other studies reported positive associations between diabetes and asthma exacerbations. However, they included potentially confounding variables and did not use laboratory testing to measure dysglycemia.

 

The purpose of this study was to establish a relationship between pre-diabetes/diabetes and the risk of asthma exacerbations. It was a retrospective observational cohort that included patients that had ICD codes with the diagnosis of asthma in at least 1 inpatient or 2 outpatient encounters. There were 5,722 patients that qualified for the cohort. Characteristics included: ages between 18 to 64 years old, enrollment of at least 1 calendar year, and a diagnosis of obesity. Other pulmonary conditions were excluded from the study. Other exclusion criteria included patients who had taken systemic corticosteroids in the previous 3 months, those who have filled hypoglycemic medications, and those who had hbA1c of below 3% and above 18%. The primary outcome was asthma exacerbations, which was defined as hospitalization, emergency department visit, or filling a prescription of oral corticosteroids after +/- 14 days of an ambulatory visit where asthma was the cause. For their statistical approach, zero-inflated negative binomial models were used to determine the association between HbA1c and rates of asthma exacerbation. They used 2 models: a count model and an inflation model. The counting model examined the rate of exacerbation which was controlled for age, sex, region, asthma controller use, Charlson Comorbidity Index, smoking, obstructive sleep apnea, and GERD. The inflation model examined the population that would not likely have an exacerbation which included age, sex, and asthma controller use. Interaction analysis was performed along with sensitivity analysis.

There was a total of 866 exacerbations over 3,868 person-years of follow-up. Patients who had HbA1c levels that were prediabetic (27%) and diabetic (33%) had higher rates than those with normal hbA1c (P= 0.01). There was no difference between patients who were younger or older than 40 (Pinteraction= 0.48), sex (P interaction= 0.33), or inhaled corticosteroid use (Pinteraction= 0.29). In the crude model, there was no association between HbA1c and asthma exacerbations. However, the relationship between HbA1c and the rate of asthma exacerbations was linear but decreased at higher values. Patients who had 9% HbA1c had fewer exacerbations but only represented about 2% of the study population. There was a 14% increase rate of asthma exacerbation for every half percentage increase in HbA1c in the linear part of the curve. 

This study presented novel data in support of the hypothesis that comorbidities, such as diabetes, can affect pulmonary function. It provided a directionality to establish a causal relationship between these two factors. Chronic hyperglycemia, hyperinsulinemia, and obesity have been associated with pulmonary modulation. One of the limitations of the study was that they excluded patients who had recent corticosteroid use which resulted in a lower rate of asthma exacerbations. Other limitations included the lack of access to socioeconomic factors, behavioral factors, or ethnicities. They also depended solely on ICD codes, which can exclude patients or misclassify them; especially when it comes to BMI. Future studies need to include patients who are older than 65 years of age with different socioeconomic factors.

Practice Pearls:

  • Prediabetes and diabetes are risk factors for obese asthma exacerbations.
  • Controlling comorbidities in patients who also have asthma can limit their asthma exacerbations.
  • This is the first study that is not cross-sectional to assess the relationship between dysglycemia and asthma exacerbations.

Wu, Tianshi David, et al. “Association Between Prediabetes/Diabetes and Asthma Exacerbations in a  Claims-Based

Obese Asthma Cohort.” The Journal of Allergy and Clinical Immunology: In Practice, vol. 7, no. 6, 2019.

 

Nour Salhab, Pharm.D. Candidate, USF College of Pharmacy