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The American Journal of Managed Care June 2018
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A Longitudinal Examination of the Asthma Medication Ratio in Children
Annie Lintzenich Andrews, MD, MSCR; Daniel Brinton, MHA, MAR; Kit N. Simpson, DrPH; and Annie N. Simpson, PhD
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Bruce C. Stuart, PhD; Sarah E. Tom, PhD; Michelle Choi, PharmD; Abree Johnson, MS; Kai Sun, MS; Danya Qato, PhD; Engels N. Obi, PhD; Christopher Zacker, PhD; Yujin Park, PharmD; and Steve Arcona, PhD
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Jonathan Hatoun, MD, MPH, MS; Emily K. Trudell, MPH; and Louis Vernacchio, MD, MS
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Klaus W. Lemke, PhD; Kimberly A. Gudzune, MD, MPH; Hadi Kharrazi, MD, PhD, MHI; and Jonathan P. Weiner, DrPH
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A Longitudinal Examination of the Asthma Medication Ratio in Children

Annie Lintzenich Andrews, MD, MSCR; Daniel Brinton, MHA, MAR; Kit N. Simpson, DrPH; and Annie N. Simpson, PhD
This longitudinal examination of the asthma medication ratio in a national sample of children has determined the predictive accuracy of a rolling 3-month ratio.
RESULTS

Demographics

Of the 9.5 million children aged 2 to 17 years present in the 2013 MarketScan data, 197,316 patients had least 1 claim for an ICS or ICS/LABA and at least 360 days of continuous enrollment after their index date. Of these patients, 60% were male and the mean age was 8.8 years; 36% were aged 2 to 6 years, 41% aged 7 to 12, and 23% aged 13 to 17. Forty-seven percent of assigned index dates were in the winter (January-March). Eighty-three percent of children had an ICS as their index controller. Ultimately, 4.5% of patients had at least 1 ED visit or hospitalization with a primary diagnosis of asthma within 18 months of their study index date (Table 1).

HEDIS Categorization of Patients in Cohort

Forty-two percent of the patients in our cohort qualified as persistent asthmatic using the HEDIS criteria. The majority of the 58% who would not qualify as such under HEDIS criteria (“non-HEDIS”) are represented in the missing AMR category in any given AMR measurement period. For example, in months 2 to 4, 85,152 of the 114,320 non-HEDIS patients had a missing AMR; 26,569 had a low-risk AMR; and 2599 had a high-risk AMR (eAppendix Figure 1 [eAppendix available at ajmc.com]).

Rolling 3-Month Versus Rolling 6-Month AMR

Using a rolling 3-month AMR calculation period and excluding the month 1 values due to the issue of AMR inflation, an average of 5% of the cohort were identified as high-risk in each calculation period, while 59% had a missing AMR (no asthma prescriptions filled during the calculation period) (Figure 1A). Using a rolling 6-month AMR calculation period and excluding the month 1 values, an average of 8% of the population were identified as high-risk in each calculation period and an average of 45% had a missing AMR (Figure 1B). Moving from a 3- to a 6-month calculation period significantly reduced the proportion of patients with missing AMRs in each given AMR calculation period. In regression analysis with the outcome variable of any ED visit or hospitalization for asthma, the 3-month AMRs had a stronger predictive ability than the 6-month AMRs (OR for 3-month AMR in months 2-4 with 3-month outcome window, 2.5; 95% CI, 2.1-2.9; OR for 6-month AMR in months 2-7 with 3-month outcome window, 1.8; 95% CI, 1.6-2.1). Table 2 presents complete results through the entire study period.

AMR Inflation

The issue of AMR inflation with our index date assignment is demonstrated graphically (eAppendix Figure 2). Because time is not accounted for in the AMR, even 1 month with a controller fill can significantly inflate a patient’s AMR for the following 11 months.

Subgroup Analysis

There was a slightly higher proportion of children 13 years and older in the high-risk AMR category compared with younger children (eAppendix Figure 3). A higher proportion of children with a winter index date maintained low-risk AMRs throughout the year (eAppendix Figure 4). Children whose index controller was an ICS/LABA rather than an ICS were more likely to have a low-risk AMR throughout the year, indicating better adherence to controller medication therapy (eAppendix Figure 5).

Do Children Stay in the Same Category Throughout the Year?

To determine if early risk-category assignment held throughout the year or if children frequently bounced in and out of categories, we followed children in each group (low-risk, high-risk, and missing, based on their assignment in the first analyzable period) through the year. The majority of children with a missing AMR in the first analyzable period continued to have missing AMRs through month 12. Similarly, the majority who were initially low-risk remained low-risk through month 12. The biggest departures from original classification occurred in the high-risk group, with only 20% (in the 3-month approach) and 39% (in the 6-month approach) remaining high-risk through month 12 (Figure 2A-F). Analyzed another way, of patients who had a high-risk AMR in any given calculation period, an average of 68% had a high-risk AMR in the following calculation period. Of patients with a low-risk AMR in any given period, an average of 84% had a low-risk AMR in the following calculation period. Finally, of patients with a missing AMR in any given period, an average of 90% had a missing AMR in the following calculation period.

How to Handle Missing AMRs

With such a large proportion of the population having missing AMRs, it was important to begin to understand how to handle these patients. The fact that they had no albuterol claims suggests that they are at low risk for exacerbation, but could they actually be at high risk and either using albuterol from previous months or not recognizing their symptoms? To help answer this question, we used each patient’s classification from the first analyzable period and calculated the proportion of patients in each category with any emergent event in study months 1 through 18. The patients with missing AMRs had the lowest proportion of events in both approaches (3.5% based on 3-month AMR classification and 3.2% based on 6-month AMR classification). This was significantly lower than the proportion with events in both the high-risk and low-risk AMR categories (P <.0001). This finding suggests that those children with missing AMRs are likely to be children with inactive asthma at low risk for exacerbation (Table 3).


 
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