Asthma represents a significant burden to the healthcare system. In 2008, almost half of the total current asthma population in the United States (12.7 of 23.3 million) experienced an asthma exacerbation, adversely affecting patients’ quality of life and increasing the likelihood of hospitalizations and emergency department (ED) visits.¹ Consequently, efforts have been made to determine quality-of-care markers that can predict future exacerbations, particularly those requiring hospital or ED visits, in order to improve asthma management and reduce this burden.

One such measure, the Healthcare Effectiveness Data and Information Set (HEDIS), is based on the proportion of health plan members with persistent asthma who are appropriately prescribed long-term control medication at least once during a given year.² Although adherence to the HEDIS measure has been associated with a lower risk of hospital and ED visits,^3,4 it has shown to be an inconsistent predictor of asthma outcomes.^5,6

Therefore, alternate measures have been proposed that more effectively assess asthma quality of care and that can more reliably predict the occurrence of exacerbations. One measure in particular, the ratio of controller-to-total asthma medication (ratio), has been shown to be a strong predictor of patient outcomes, asthma-related hospitalizations, and ED utilization,^5,7-11 and a better quality-of-care marker than the HEDIS measure.¹⁰ Studies examining the predictive ability of this marker incorporate a 1-year measurement period that is consistent with the HEDIS performance measure. This period is valid given that the ratio might not be appropriate for patients who do not have persistent asthma. However, a 1-year measurement period prevents rapid interventional adjustments. It is not known whether a shorter measurement period would affect the predictive ability of the ratio. Because of the restrictive nature of the persistent asthma measure and the need for defining a population in a study with shorter observation times, an asthma population at risk for uncontrolled asthma or asthma exacerbations was defined for this study. At-risk patients were defined as those that meet the treatment and symptom (albuterol use as the proxy) criterion of having at least mild persistent asthma according to National Asthma Education and Prevention Program guidelines.²

Most of the studies on the ratio have been performed in persistent asthma patients from commercially insured databases across age groups. Studies in children and those from the Medicaid population are limited. It is important to study these populations because Medicaid patients are representative of a population that is more likely to have asthma and asthmarelated adverse events, specifically individuals who are younger, are female, and have lower socioeconomic status.^12-14 Among those insured by Medicaid, a higher percentage of patients have asthma and poorer asthma control compared with those who have private insurance or are uninsured.^15,16 Medicaid coverage was found to be independently associated with poor asthma control in children, and controller medication underuse among Medicaid- covered children is widespread.^17-20 Studies have shown that children in Medicaid were more likely to be admitted to the ED or hospital for asthma compared with privately insured children.^17,21

In this study we examined the predictive ability of the ratio in pediatric and adult populations at risk for asthma exacerbations using both commercially insured and Medicaid databases. The primary goal was to determine an optimal value for the ratio that is associated with a significant difference in predicting future exacerbations. We also examined the correlation between incremental unit changes in the ratio and the risk of having an exacerbation. Lastly, we identified an optimal time frame for measuring the ratio to accurately predict the risk of future exacerbations.

METHODS

Study Population and Design

This study was a retrospective analysis of 2 databases, the Ingenix Impact National Managed Care Database (commercially insured) and the MarketScan Medicaid Database. The data used were from January 1, 2003, to either June 30, 2007 (Medicaid), or June 30, 2008 (commercially insured). The commercially insured database utilized the integrated medical and pharmacy administrative claims of more than 98 million lives spanning 9 census regions. The Medicaid database utilized nearly 22 million enrollees across 6 states. The initial study population identified included patients with at least 1 pharmacy claim for any type of asthma medication excluding oral corticosteroids (OCSs) during the enrollment period from January 1, 2004, to either June 30, 2005 (Medicaid), or June 30, 2006 (commercially insured). The 1-year period before the enrollment period (preindex period) was used for baseline assessment and to ensure the presence of asthma. The postindex period had 2 parts: 1 to calculate the ratio (the optimal assessment period) and a subsequent 12-month follow-up period. The optimal assessment period was varied using 3-, 6-, and 12-month periods to allow for sufficient time to accurately calculate the ratio.