Predicting frequent asthma exacerbations using blood eosinophil count and other patient data routinely available in clinical practice

Purpose: Acute, severe asthma exacerbations can be difficult to predict and thus prevent. Patients who have frequent exacerbations are of particular concern. Practical exacerbation predictors are needed for these patients in the primary-care setting.  Patients and methods: Medical records of 130,547 asthma patients aged 12–80 years from the UK Optimum Patient Care Research Database and Clinical Practice Research Datalink, 1990–2013, were examined for 1 year before (baseline) and 1 year after (outcome) their most recent blood eosinophil count. Baseline variables predictive (p<0.05) of exacerbation in the outcome year were compared between patients who had 2+ exacerbations and those who had 0 or 1, using uni- and multivariable logistic regression models. Exacerbation was defined as asthma-related hospital attendance/admission (emergency or inpatient) or acute oral corticosteroid (OCS) course.  Results: Blood eosinophil count >400/μl (versus ≤400/μl) increased the likelihood of 2+ exacerbations >1.4-fold [odds ratio (OR): 1.48 (95% confidence interval: 1.39, 1.58); p<0.001]. Variables that increased the odds by up to 1.4-fold (p<0.05) included increasing age (per year), female gender (versus male), being overweight or obese (versus normal body mass index), being a smoker (versus nonsmoker), having anxiety/depression, diabetes, eczema, gastroesophageal reflux disease, or rhinitis, and prescription for acetaminophen or nonsteroidal anti-inflammatory drugs. Compared with treatment at British Thoracic Society step 2 (daily controller ± reliever), treatment at step 0 (none) or 1 (as-needed reliever) increased the odds by 1.2- and 1.6-fold, respectively, and treatment at step 3, 4, or 5 increased the odds by 1.3-, 1.9-, or 3.1-fold, respectively (all p<0.05). Acute OCS use was the single best predictor of 2+ exacerbations. Even 1 course increased the odds by >3-fold [OR: 3.75 (3.50, 4.01); p<0.001], and 3+ courses increased the odds by >25-fold [OR: 25.7 (23.9, 27.6); p<0.001].  Conclusion: Blood eosinophil count and several other variables routinely available in patient records may be used to predict frequent asthma exacerbations.