Study design and data sources
We conducted a retrospective cohort study using an anonymized data from April 2015 to September 2020 in Hachioji City, Tokyo, Japan. The city is located on the western side of Tokyo and its population was approximately 578,000 in 2015, of whom 25.0% were aged ≥ 65 years [20]. We received the data following an agreement from a collaborative research project between the municipality and the affiliation of the first author. All data were anonymized, and unique numbers were assigned to each insured person to connect the medical and LTC insurance claims data.
This study used medical insurance claims, LTC insurance claims, LTC insurance premium, and care needs certification data obtained from the city. Medical insurance claims data include beneficiaries of the national health insurance system or the medical care system for older people in later stages of life. In Japan’s medical care insurance system, 70% of people aged 65–74 years were beneficiaries of the national health insurance system in 2015 [21], and all those aged ≥ 75 years were enrolled in the medical care system for older people in the later stages of life [22]. Although this study did not include people aged 65–74 years who were able to work until just before the first LTC certification, it is thought that the influence of previous working conditions on assistive product use is small after adjusting other covariates among older people with LTC certification. Therefore, we considered the selection bias among people aged 65–74 years, of which 70% were beneficiaries, to be minimal.
Participants
The eligibility criteria were as follows: (1) beneficiaries of the national health insurance or medical care system for older people in the later stages of life who were first certified as having LTC needs between April 2015 and March 2020 and (2) aged ≥ 65 years at the first certification. We selected people who were first certified because some assistive products used by home adaptation or purchase services are often used only once after being certified for LTC needs [23]. To avoid including participants who had moved from another municipality and had the first certification at previous municipalities, we confirmed that the LTC certification application codes of the first-time certifiers were “new” and the previous certification period was thus null.
The exclusion criteria were as follows: (1) lack of LTC insurance premium data; (2) those who were not insured by the national health insurance or medical care system for older people in the later stages of life within one year before the first certification, which means those who did not have one-year baseline data; and (3) those who used LTC facility services for six consecutive months within the six months after the first certification, because those who use LTC facility services may use the assistive products possessed by the facility and do not generally rent or purchase assistive products.
Measurements
The primary explanatory variable was the presence or absence of COPD, which was determined within one year before the first certification (i.e., baseline period). We defined participants with COPD as having both a COPD diagnosis and COPD-related prescriptions for daily dyspnea. First, COPD diagnosis was defined by the International Classification of Diseases and Related Health Problems, 10th revision, codes J41–J44 (not including suspected diagnosis) for two or more months within the first certification [4, 24,25,26]. Second, we also identified long-acting muscarinic antagonist, long-acting β2 agonist prescriptions, or both (including combination products) for two or more months as treatments for daily dyspnea of COPD [5].
The outcome variable was assistive product utilization delivered as Japanese LTC insurance services during the six months following the first certification because the validity period for newly certified care needs is usually six months [27]. In Japan, older people requiring LTC can access assistive products through the LTC insurance system in three ways if the insurers accept its necessity: (1) by receiving housing adaptation services, such as the installation of handrails; (2) rental services of assistive products, such as wheelchairs and electronic beds; and (3) purchasing services, such as bathing aids (Additional File 1) [19]. There are restrictions on the rental of some assistive products, such as wheelchairs, based on the LTC needs levels: rental is permitted for people with LTC needs levels 2 or higher and for those with LTC needs levels 1 or lower with valid reasons for rental, such as daily fluctuations in symptoms, sudden deterioration of the condition, or physician’s instructions based on the medical condition [28]. In this study, we selected assistive products for environmental modifications (handrails/grab bars and ramps), mobility (canes, walkers, and wheelchairs), and self-care activities in daily life (electronic beds and bathing aids) (Additional File 1). Three medical professionals (an occupational therapist, physical therapist, and nurse) familiar with assistive products selected only assistive products that were expected to help reduce energy consumption for older people with COPD and excluded those that compensate for memory functions, such as motion sensors to prevent falls or wandering. We did not include assistive products such as portable toilets and bathtubs with a low utilization rate at less than 1%.
We also identified the following sociodemographic and physical factors that were expected to be associated with assistive product utilization [23, 29, 30]: age, sex (male or female), household income (low or middle to high), care needs level, use of home oxygen therapy (used or not), diseases other than COPD (present or absent), and date of first LTC certification (April 2015 to March 2018 or April 2018 to March 2020). We examined LTC insurance premiums for the year of the certification to classify the participants’ household income as economic status. If the participant and all family members were exempt from residential taxation based on their income, the household income was classified as low income, and the rest were classified as middle-to-high income [31]. The LTC need levels were selected from the certification data for LTC needs levels. LTC needs levels were categorized as care supports level 1 (least dependent) and 2, or care needs level 1 to 5 (most dependent) [17]. We also selected the use of oxygen therapy using certification data for LTC needs levels through a question asking whether the patient had received oxygen therapy in the past 14 days. We examined comorbidities expected to be associated with LTC needs certification based on medical claims one year before the first certification, including cancer, cardiac diseases, cerebrovascular diseases, dementia, diabetes, fractures, joint diseases, Parkinson’s disease, and visual or hearing impairment, according to a previous study [32]. We divided the date of the first LTC certification into before and after April 2018 as medical and LTC fees were revised in April 2018 in Japan, which included the setting of an upper limit on the rental price of assistive products.
Statistical analysis
First, we compared the basic characteristics and the assistive product utilization between the participants with or without COPD, using the Mann–Whitney U or χ2 test. We then conducted multivariable logistic regression analyses to examine the associations between the utilization of each assistive product and COPD using all covariates with stratifying those requiring low care levels (care supports level 1 to care needs level 1) and those requiring middle to high care levels (care needs level 2 to 5), because it was expected that assistive product utilization would differ according to their care needs levels and because, as previously mentioned, some assistive products such as wheelchairs and electric beds can only be rented for care-needs levels 2 or over in the Japanese LTC system [28]. Therefore, those with care supports level 1 to care needs level 1 were classified as those requiring low care group, and those with care needs level 2 or higher were classified as those requiring middle to high care group. In multivariable logistic regression analyses, age was treated as a continuous variable, while other variables were treated as categorical variables. Care supports level 1 and care needs level 1 were set as reference for the analyses in participants who required partial care and in those who required total care, respectively. Additionally, we conducted sensitivity analyses excluding participants with care needs levels 5 from those with middle to high care levels, because the condition of completely bedbound care might override the characteristics of COPD. All statistical analyses were performed using Stata/MP 16.0 for Windows (Stata Corporation, College Station, TX, USA). Statistical significance was defined as a p-value < 0.05.