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Clinical and Economic Burden of Elevated Blood Eosinophils in Patients With and Without Uncontrolled Asthma

Julian Casciano, BS; Jerry Krishnan, MD, PhD; Zenobia Dotiwala, MS; Chenghui Li, PhD; and Shawn X. Sun, PhD

BACKGROUND
The European Respiratory Society and American Thoracic Society (ERS/ATS) published guidelines in 2014 for the evaluation and treatment of asthma. These guidelines draw attention to management of patients with asthma that remains uncontrolled despite therapy. One phenotypic characteristic of therapy-resistant asthma is eosinophil elevation. It is important to better understand the burden of care gaps in this patient subgroup in order to support improved treatment strategies in the future.

OBJECTIVE
To quantify the economic burden of asthma patients with and without peripheral blood eosinophil elevation.

METHODS
A retrospective cohort study was conducted using data from patients aged 12 years or older with a diagnosis of asthma using electronic health records of over 2 million patients between 2004-2010. Patients with a diagnosis of chronic obstructive pulmonary disease, Churg Strauss syndrome/Wegener’s granulomatosis, eosinophilia, cystic/pulmonary fibrosis, allergic bronchopulmonary aspergillosis, or lung cancer in the 12-month period before the date of asthma diagnosis were excluded. Patients with asthma were followed for 12 months after their initial asthma diagnosis to identify those with controlled versus uncontrolled asthma based on ERS/ATS criteria. Patients with at least 1 peripheral blood eosinophil test result of ≥ 400 cells/μL were classified as those with elevated eosinophils. Total annual paid-claim cost was compared by eosinophil levels within the controlled and uncontrolled asthma subgroups. Costs were adjusted to 2015 U.S. dollars. Patients were stratified by control level, and generalized linear modeling regressions were used to assess the magnitude of increase in cost of the elevated eosinophil group.

RESULTS
A total of 2,701 patients were included in the study, of which 17% had uncontrolled asthma and 21% had elevated eosinophils. The mean total annual cost of patients with uncontrolled asthma was more than 2 times the cost of those with controlled asthma ($18,341 vs. $8,670, P < 0.001). Patients with uncontrolled asthma in the elevated eosinophil group had almost double the total cost ($28,644 vs. $14,188, P = 0.008) compared with those with blood eosinophil levels in a normal range. Similarly, patients classified as those with controlled asthma in the elevated eosinophil group had almost twice the average costs as those without elevated eosinophils ($14,754 vs. $7,203, P < 0.001). Uncontrolled asthma with elevated eosinophils had 4 times greater hospital admissions and over 4 times higher total costs than controlled asthma without elevated eosinophils. Among patients with uncontrolled asthma, patients with elevated eosinophils had a 53% increase in mean cost ($17,723 vs. $11,581, P < 0.001) compared with patients without elevated eosinophils. Among patients with controlled asthma, patients with elevated eosinophils had a 62% increase in mean cost ($8,897 vs. $5,486, P < 0.001) compared with patients without elevated eosinophils.

CONCLUSIONS
Elevated peripheral blood eosinophil level is associated with higher cost irrespective of disease control status.

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Progression to Uncontrolled Severe Asthma: A Novel Risk Equation

Julian Casciano, BS; Jerry Krishnan, MD, PhD; Mary Buatti Small, MS; Chenghui Li, PhD; Zenobia Dotiwala, MS; and Bradley C. Martin, PharmD, PhD

BACKGROUND
Recently published asthma guidelines by the European Respiratory Society and the American Thoracic Society (ERS-ATS) define severe disease based on medication use and control level. These guidelines also emphasize that asthma severity involves certain biomarker phenotypes, one of them being eosinophilic phenotype. The quantification of the influence of eosinophil level toward predicting disease severity can help decision makers manage therapy better earlier.

OBJECTIVE
To develop a risk-scoring algorithm to identify patients at greater risk of developing uncontrolled severe asthma as defined by ERSATS guidelines.

METHODS
Data on asthma patients were extracted from the EMRClaims+ database from January 2004 to July 2011. Patients with continuous enrollment 12 months before and after the date of the first encounter with a diagnosis of asthma (index date) with at least 1 blood eosinophil test result in the 12 months after the index date, but before the development of uncontrolled severe asthma or the study end date, were included. Uncontrolled severe asthma was defined as the first date on which all criteria of the ERS-ATS definition were first satisfied in the 12 months after the index date. Age (≥ 50 years vs. < 50 years), race, and sex were measured at index, and the Charlson Comorbidity Index (CCI) score (> 0 vs. 0) was measured in the pre-index period. Elevated eosinophil level was defined as a test result with ≥ 400 cells/μL. The study cohort was randomly split 50-50 into derivation and validation samples. Cox proportional hazards regression was used to develop the risk score for uncontrolled severe asthma using the derivation cohort with independent variables of eosinophil level, age, sex, race, and CCI. A bootstrapping procedure was used to generate 1,000 samples from the derivation cohort. Variables significant in ≥ 50% of the samples were retained in the final regression model. A risk score was then calculated based on the coefficient estimates of the final model. C-statistic was used to test the model’s discrimination power.

RESULTS
The study included 2,405 patients, 147 (6%) of whom developed uncontrolled severe asthma. Higher eosinophil level and CCI score > 0 were significantly and independently associated with an increased risk of uncontrolled severe asthma in the derivation cohort (HR = 1.90, 95% CI = 1.17-3.08 and HR = 2.00, 95% CI = 1.28-3.13, respectively); findings were similar in the validation cohort. Total risk score was categorized as 0, 2, and 4. All models showed good C-statistics (0.79-0.80), indicating favorable model discrimination. There was a significantly greater number of patients with uncontrolled severe asthma in the risk score segments of 2 and 4 compared with 0 (each P < 0.0001).

CONCLUSIONS
A risk stratification tool using peripheral eosinophil counts and CCI can be used to predict the development of uncontrolled severe asthma.

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