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Predictors of Healthcare Costs After Initiating Dabigatran Versus Warfarin

The study found no mean difference in all-cause healthcare costs for patients with newly diagnosed nonvalvular atrial fibrillation initiating treatment with dabigatran versus warfarin.
Published Online: Feb 02,2018
Sabyasachi Ghosh, MS; Jason P. Swindle, PhD, MPH; John C. White, DPM, MS; Stephen D. Sander, PharmD; Cheng Wang, MD, PhD
METHODS
Study Design and Data Source
This was a retrospective cohort study of commercial and Medicare Advantage with Part D enrollees. The study utilized administrative claims data from a large national US health plan from April 1, 2009, through November 30, 2013 (study period). All data were accessed in accordance with the Health Insurance Portability and Accountability Act rules.

Patient Identification and Study Cohorts
Patients with evidence of newly diagnosed NVAF initiating therapy with either dabigatran or warfarin were identified using enrollment data and medical and pharmacy claims from October 1, 2010, through November 30, 2012. Patients were selected for inclusion in a sequential manner:

1. Evidence of AF defined as at least 1 inpatient stay, 2 physician office visits, 2 emergency department (ED) visits, or a combination of office visit and ED visit on distinct service dates, with a diagnosis code for AF (International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis code 427.31, in any position) from October 1, 2010, through August 31, 2012 (identification period).21 The AF index date was the date of the first qualifying claim with a diagnosis code for AF. Patients were aged ≥18 years as of AF index date, had 12 months continuous enrollment (no gaps >45 days) with medical and pharmacy benefits prior to AF index date, and had no medical claims with a diagnosis code for AF within 12 months prior to AF index date. 

2. Excluded were patients with ≥1 medical claim with evidence of valvular heart disease or hyperthyroidism (reversible cause of AF22) prior to AF index date, and patients with evidence of transient AF within 3 months prior to AF index date.  

3. Newly initiating OAC therapy with dabigatran or warfarin by meeting all of the following criteria: ≥1 pharmacy claim for warfarin or dabigatran on the AF index date or during the 3-month period following AF index date; the date of the first claim was defined as the OAC index date; continuous enrollment during the period of AF index date through OAC index date; and no pharmacy claims for any OAC for 12 months prior to OAC index date (baseline period).  

4. Remaining patients were required to have ≥30 days follow-up after OAC index date. The follow-up period began on the OAC index date and ended at the earliest occurrence of the following: (a) end of study period; (b) death; (c) switch to another OAC without a claim for ischemic stroke and/or bleed; (d) discontinuation of index OAC with a gap >30 days from the run-out of the last fill without a claim for ischemic stroke and/or bleed; (e) end of continuous enrollment in health plan; or (f) greater than 364 days following OAC index date. Twelve months follow-up is similar to recent studies comparing resource utilization and costs between dabigatran and warfarin cohorts;12,21 it also aligns with year budget allocation cycle by different payers and providers across the United States.

Patients were then assigned to 2 mutually exclusive study cohorts according to index OAC. Relevant codes for conditions used in patient selection are shown in eAppendix Table 1A (eAppendices available at AJPB.com).

Model Variables
Follow-up Healthcare Costs
Two measures of all-cause healthcare costs (combined health plan and patient paid amounts) were computed during the variable length of follow-up period: (a) episode-based total costs (all-cause medical and pharmacy) were determined using ETG methodology16 and included episode-based predictors of healthcare costs; (b) all-claims total costs (all-cause medical and pharmacy) were computed and only included non–episode-based predictors of healthcare costs. Both measures of costs were computed as per-patient per-month (PPPM) costs to adjust for variable length of follow-up. Costs were adjusted to 2013 US dollars using the annual medical care component of the Consumer Price Index to account for inflation between 2009 and 2013.23

Predictors of Healthcare Costs
Patient severity was captured using 2 measures: baseline CCI score for all-cause claims cost analysis and baseline ERG risk score for all-cause episode-based cost analysis. The CCI score24-26 is a proxy for likelihood of mortality according to the burden of comorbidity; scores were grouped as 0, 1-2, 3-4, and ≥5. The ERG risk score assesses the prospective risk of healthcare utilization and costs according to comorbidities and medical complications. ERG risk scores were determined using ETG methodology, which defines episode of care for measurement of healthcare costs using diagnosis, procedure, and revenue codes; and National Drug Code numbers to formulate clinically homogeneous episodes of care (eAppendix Figure 1A).16 The ETG methodology allows for case-mix adjustment, clinical homogeneity, episode building, concurrent and recurrent episodes, and shifting episodes.27 ETGs are then mapped to ERGs for each patient. Next, individual ERG risk scores are computed by summing weights assigned to each ERG and to the patient’s demographic and healthcare resource utilization profile.28 The ETG/ERG methodology is used by several health plans29-35 and allows for customized categorization of ERG scores, but there is no guidance in current literature on grouping ERG risk score into specific categories. For this study, scores were grouped, a priori, into 6 categories: ≤2.0; 2.1 to 4.0; 4.1 to 6.0; 6.1 to 8.0; 8.1 to 10.0; and >10.0. A score of 1.0 indicates risk comparable with that of the overall population, while a score of 2.0 or greater indicates a 2-fold or greater risk of higher healthcare resource utilization and costs.

Additional variables considered for inclusion as predictors in multivariable modeling of follow-up costs were age, sex, geographic region, health plan type, baseline healthcare costs, and durations of treatment delay and follow-up for the all-claim cost analysis. For the episode-based cost analysis, all but age, gender, and baseline healthcare costs were included because ERG risk score accounts for these measures.




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