The final study sample involved 8554 patients. The demographic and clinical characteristics of the COPD population taking maintenance medications as measured in the identification period (Year 1) are reported in . The mean age of the population was 70.1, with 79% of patients aged 65 years or older. The population was mainly made up of Medicare health plan members (96.5%), and was split evenly between the genders. The sample consisted predominantly of white members residing in the southern United States, with nearly half (49%) of the sample reporting a medium income level. The medium income level was made up of incomes between $33,541 and $52,480 after the sample income was divided into tertiles.
For all patients, the mean DCI score was 1.9 (standard deviation, 1.8; range, 0–16). Among the comorbidities used to calculate the DCI score, the top comorbidity was related COPD diagnoses (23.0%, including chronic pulmonary heart disease, COPD and allied conditions other than 491.x, and respiratory conditions due to external agents). This was closely followed by diabetes without complication and congestive heart failure (22.2% and 18.3%, respectively). Peripheral vascular disease and renal disease were also included in the top five comorbidities (11.4% and 9.6%, respectively).
Among the maintenance medications taken by the patients in this study, 100% of the population had filled one or more prescriptions for ICS, 52.3% for ICS and LABA combination drugs, 43.4% for LAMAs, and 24.9% for triple ICS, LABA, and LAMA combination therapy. These categories were not mutually exclusive – that is, a patient may have been included in more than one category. In addition to COPD maintenance medications, the majority of patients (84.2%) filled one or more prescriptions for antibiotics during the course of the year, 61.8% were treated with oral or parenteral corticosteroids, and 41.2% were receiving long-term oxygen therapy.
The proportion of patients with each type of exacerbation, as well as number of exacerbations during the follow-up year, is provided in and is categorized as patients with one or more exacerbations, those with two or more exacerbations, and those aged 65 years or older. Of the overall population on maintenance medications, 49.8% had any type of exacerbation. Within this group, 13.9% had severe exacerbations only, 29.1% had moderate exacerbations only, and 6.8% had both a severe and a moderate exacerbation. The overall population was also stratified into three patient categories: (1) patients with one or more exacerbations during the baseline period, (2) patients with two or more exacerbations during the baseline period, and (3) patients aged 65 years or older. As with maintenance medications, these subgroups were not mutually exclusive. As expected, patients with two or more exacerbations during the baseline period had the highest rate of exacerbations per patient in the follow-up year among the three subgroups, followed by patients with one or more exacerbations (). The rates of exacerbations per patient per year during the follow-up year for all subgroups were as follows: 1.26 for the subgroup with one or more exacerbations at baseline, 1.77 for the subgroup with two or more exacerbations at baseline, and 0.99 for patients aged 65 years or older. Rates of exacerbations for subgroups with a history of exacerbations at baseline were significantly different from the overall population (P < 0.05, ).
Factors associated with annual cost of exacerbation by type
Proportion of patients with exacerbations and number of exacerbations in Year 2 (follow-up period)
In line with the observed numbers of filled prescriptions reported in , annual COPD-related utilization in the overall population reported in was dominated by pharmacy claims (91.6%), which were closely followed by physician office visits (75.8%). Approximately one-fifth of the cohort (20.6%) had COPD-related inpatient hospitalizations, and 13.9% had emergency room visits during the study time period. As expected, patients with two or more exacerbations dominated consumption in all utilization categories.
Annual chronic obstructive pulmonary disease (COPD)–related utilization and costs for COPD patients on maintenance medications
Patients with two or more exacerbations also led COPD-related unadjusted annual costs (). Specifically, inpatient costs for the subgroup were almost double that for the overall population ($2835 versus $1576). Total COPD-related annual costs were $6381 for the subgroup with a history of two or more exacerbations, versus $4069 for the overall population.
Patients who experienced both severe and moderate exacerbations led in adjusted COPD-related costs and in total health care cost per year (). After adjustment, total COPD-related costs were similar to unadjusted total costs for each of the one or more exacerbation and two or more exacerbation subgroups and for the group aged 65 years or older. COPD-related health care costs were substantially higher for all three groups than for the no exacerbation group ($4875, $6550, $4050, versus $1425, respectively), with a similar trend observed for total health care costs ($20,418, $23,346, $18,038 versus $11,747, respectively).
Adjusted annual chronic obstructive pulmonary disease (COPD)–related and total health care costsa in follow-up year
Factors associated with the annual cost of exacerbation are provided in . Notably, experiencing a moderate or severe exacerbation was associated with incrementally higher cost than the cohort with no exacerbation. Exponentiation of the coefficients from the GLM suggested that, all else being equal, the cost ratio for a patient with a severe exacerbation relative to a patient with no exacerbations was 2.7, and for a patient with a moderate exacerbation versus a patient with no exacerbations the cost ratio was 1.17. Long-term oxygen use, a proxy for severe disease, was associated with a cost ratio of 1.24. Each of the maintenance medications was also associated with higher health care costs, but coefficients were smaller than for long-term oxygen use. Cardiovascular disease was associated with a cost ratio of 1.69, and diabetes with a cost ratio of 1.46. The parameter estimate for age was close to zero (but negative), and statistically significant. This was an unexpected result, but it may reflect the fact that costs for commercial health plan members are higher than for Medicare members.