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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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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.
Ratio Calculation

Using the formula of number of controller medication claims/(number of controller medication claims + number of rescue medication claims), an AMR was calculated for each patient in each month from the index date to study month 12. AMRs can range from 0 (only rescue medication claims) to 1 (only controller medication claims) or be “missing” (no rescue or controller medication claims) for any given period. Leukotriene-receptor modifiers were included as controllers in the AMR calculation if there was not also an ICS-containing medication claim that month, but they were not included as index controllers. This decision was made to ensure that our cohort represented children with persistent asthma who received first-line guideline-recommended therapy for that diagnosis. Oral albuterol was not included as a rescue medication.

Similar to previous studies, we first calculated fixed 12-month, 6-month, and 3-month AMRs for each patient for the 12 months after the index date. Therefore, each patient has one 12-month AMR, 2 fixed 6-month AMRs, and 4 fixed 3-month AMRs. Next, we calculated rolling AMRs for each patient. Rolling 3-month AMRs were calculated using months 1 to 3, 2 to 4, 3 to 5, and so on. Rolling 6-month AMRs were calculated using months 1 to 6, 2 to 7, 3 to 8, and so on.

Based on previous study results, AMRs were classified as high-risk (<0.5), low-risk (≥0.5), or missing for each calculation period. Because of our definition of index date, the AMR values for the first period (those that include month 1) are artificially inflated. Identifying this phenomenon influenced further analytical decisions.

Population-level AMR distribution through 12 study months was plotted using stacked bar charts. Patients in each category (high-risk, low-risk, and missing) for the first analyzable rolling 6-month and 3-month period were tracked at the population level over the course of the year. We also determined the proportion of patients who remained in the same risk category from one month to the next.

Subgroup Analysis

To identify differences by patient characteristics, AMR classification changes over time were also assessed by age group, season of index date, and category of index controller (ICS vs ICS/long-acting β agonist [LABA]).

Outcome Definition

ED visits and hospitalizations with a primary diagnosis of asthma (ICD-9 code 493.XX) were identified. Having any ED visit or hospitalization for asthma in a given period was the primary dichotomous outcome for this study. Future studies should include more in-depth analyses of the rolling AMR’s relationship to this outcome as well as individual outcomes of ED visits, hospitalizations, and oral steroid dispensing events.

Preliminary Outcome Analysis

To begin to understand how patients with missing AMRs should be classified in future interventional studies, we compared proportions of patients with any ED visit or hospitalization for asthma among those classified as having high-risk, low-risk, and missing AMRs in the first analyzable rolling 3-month and 6-month periods (months 2-4 and months 2-7, respectively). Chi-square tests were used to identify any statistically significant differences.

Determining the Relative Strength of Association of 3-Month Versus 6-Month Rolling AMRs With Events

Simple logistic regression models with the outcome of ED visit or hospitalization in 3-month and 6-month outcome windows were built for rolling 3-month AMRs and rolling 6-month AMRs. Comparisons of odds ratios (ORs) between the 3-month AMRs and 6-month AMRs were used to quantify strength of association to help inform the decision of which calculation strategy to use in subsequent analyses.


 
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