Comparison with existing literature
We found that sex influenced service use in the adjusted model, with higher odds of ED visits and hospital admissions among males. The effects of sex on healthcare service use and cost have been demonstrated in a number of studies from Canada and other high- and middle-income countries (24, 41–45), with the results generally showing the opposite to our findings – i.e., greater use/cost in women. Reproductive and sex-related morbidity and mortality have been found to account for sex differences in health care costs in one Canadian study (45), but studies on other populations have found these factors explain some but not all service use/cost differences (41, 44). Sex differences may also reflect use of different types of services. Friberg et al. (44) found that women were more likely to receive primary care while men were more likely to receive inpatient (hospital) care, and Bertakis et al. (41) found women had higher healthcare service use including ED visits but not hospitalizations after adjusting for health and socio-economic status. Canadian studies focused on ED use show little evidence of sex differences, particularly among older adults aged 65 + years of age (46, 47). Our findings are nevertheless consistent with a number of studies showing that older men in particular dominate resource-intensive health care (12, 44, 45, 48). This may reflect the kinds of conditions men are most likely to have or their higher mortality risk (due to a shorter life expectancy) thus leading to the need for more demanding (acute care) services (44). It may also reflect a reluctance by men to seek health care except in cases of acute/serious illness (49).
Our study found independent age effects as well, with higher odds of ED visits and hospital admissions in older adults (age 75–84 vs 65–74). Ample evidence demonstrates the importance of age as a determinant of healthcare service use (44), although many studies do not control for multimorbidity in examining the impact of age on service use (or vice versa), resulting in uncertainty regarding the independent influence of these factors. The age effect observed in our study may reflect differences in access to or preferences for services, or the severity of underlying conditions. It may also reflect the presence of other conditions or symptoms common in older adults that require receipt of healthcare services but are not captured by measures of chronic illness (e.g., frailty, incontinence, falls, pain). Age effects on hospital use independent of multimorbidity were also reported by Payne et al. (50) in their retrospective study of a large (n = 180,815) Scottish general population cohort, and have been seen in studies of specific disease cohorts, such as those with diabetes (51, 52).
Overall, we did not find a significant age/sex interaction influencing acute care service use, consistent with other studies reporting few or no significant age/sex influences, including the study by van den Bussche et al. (19) looking at ambulatory care services and Hessel et al. (24) who studied general practitioner and specialist services. The drop we observed in ED visits for males in the highest multimorbidity/age category (4+, 75–84) compared to the lower multimorbidity/age category (2–3, 75–84) is unusual, and we are aware of only one other study with a similar finding – i.e., Librero et al. (53) found that patients in the highest morbidity group (5 + conditions) were significantly less likely to have an ED visit (OR = 0.51) compared to those without chronic conditions, whereas patients with moderate morbidity burden (1–2) had significantly higher chances (OR = 1.24). The Lehnert et al. (13) review noted that the Librero et al. (53) study was unusual, with all others showing a positive association (ranging from weak to strong) between number of chronic conditions and ED visits. Our finding of a drop in ED visits in males in the highest multimorbidity/age category suggests that further research may be helpful – e.g., men in the highest multimorbidity category may spend more time in the hospital thus have less time to visit the ED, and women may show this same pattern in an older age cohort due to their longer life expectancy (e.g., 85+, excluded from our study).
Socioeconomic status shaped acute care service use in our adjusted analysis. Lower household income and education were each associated with higher odds of ED visits, and lower household income was associated with higher odds of hospital admissions. This finding is consistent with another Canadian study that found that the association between the level of multimorbidity and healthcare costs was greater at higher levels of neighbourhood marginalisation (7). It is also consistent with other studies which use a range of measures of socioeconomic status at the individual and/or regional level, including deprivation quintiles, education, and free medical care (17, 18, 54). It is important to note that the socioeconomic gradient seen in this study exists despite Canadian residents having access to near-universal health insurance coverage, suggesting that despite the fact that Canada has a national system of health and social services, older adults with lower socioeconomic status are less likely to use acute care services. Also important is that the socioeconomic gradient found in our study is independent of multimorbidity, which itself is typically more prevalent in socioeconomically-deprived populations (55). It may be that individuals living in marginalized areas face barriers to accessing healthcare services (56), with cascading effects in terms of developing poorer health outcomes and requiring more expensive healthcare expenses (7). Further research is needed to better understand the socioeconomic gradient relating to acute care service use within the context of the Canadian healthcare system.
Immigrant status was independently associated with acute care service use in our adjusted analysis. Non-immigrants had higher use of both acute care services compared to immigrants, with larger differences for ED use compared to hospitalizations. Roberge et al’s study on ED use (57) found lower service use in immigrants compared to non-immigrants in their study of Canadian residents from Quebec. The longitudinal nature of their study was helpful in understanding the possible reasons for this difference - e.g., it showed that recent immigrants were healthier and younger than the general population, and over time ED use in immigrants became similar to non-immigrants such that after 10 years service use was identical in the two groups (57). Other research suggests that lower service use by immigrants could be a reflection of access barriers due to language or lack of knowledge (58), which is further supported by reports of unmet healthcare needs among immigrants (59). This literature collectively highlights the complexity of this phenomenon and the need for further study.
Geographic location influenced ED use but not hospitalizations in our adjusted analysis, with higher ED use among rural versus urban residents. Other Canadian studies have observed greater use of ED services in rural areas (57, 60). This has been attributed in part to the way services are organized in rural areas, with rural physicians tending to practice in emergency departments and hospitals and thus encourage patients to use these services to preserve continuity of care (61, 62). The vast majority (88%) of people in the study by Roberge et al. (57) reported having consulted a health professional before going to the ED and were advised by them to go there, perhaps reflecting the organization of primary care and/or urgency of the healthcare need. This study also found that fewer people with a regular source of primary health care went to EDs, and suggested that this may be due to the increased likelihood of rapid service access for immediate needs and benefits linked to continuity of care (63, 64). However, another Canadian study found that those with a regular doctor were as likely to report ED use as those without one, and that heavy users of primary care services were equally heavy users of ED services (60, 65). Similarly, a large US study found that those who lacked a regular doctor were less likely to be a frequent ED user (66). Therefore, having a usual source of care does not guarantee reduced ED use and lack of access to usual care does not necessarily increase ED use, highlighting the importance of other drivers such as the patient’s health status, perceptions of need, and the organization/accessibility of primary care services. The finding that users of EDs in rural areas of Canada are less sick compared to those in urban areas (57) suggests that factors linked to nonurgent use reported in other studies may be relevant, notably perceived need for specialized services and access barriers (67, 68). Clearly, EDs and hospitals operate differently in urban and rural settings, thus it is important to understand this context in order to correctly interpret acute care use and design interventions to optimize it.
Self-perceived physical health and daily functioning (IADLs in our study) were each associated with acute care service use in the adjusted analysis, with low/poor self-perceived health and functionality linked to higher ED use and hospitalizations. Previous research is consistent with our finding (69–72), and also shows that adding functional status to health status measures derived from administrative data improves the ability to identify high risk/high-cost system users (69, 73). Studies also show that, compared to users of primary care services and medical clinics, more people will seek ED services for health problems causing pain, limitations in their daily functioning, and risk of complications (57, 62, 74). Collectively, this evidence suggests that chronic illness alone is insufficient in explaining healthcare service use. Capturing a broader range of health status measures may in fact hold the key to designing future interventions that are effective in addressing service needs/use.
Self-perceived mental health was associated with hospitalization but not ED use in our adjusted analysis, with lower perceived mental health associated with fewer hospitalizations. Evidence exists linking lower self-perceived mental health to higher use of mental health services, complementary services (e.g., chiropractic, acupuncture), and general practice (75); however, the evidence is weaker in relation to use of hospitalizations. Remes et al. (76) found that anxiety was not associated with hospital admissions unless it was comorbid with depression, and other studies show that self-reported mental health was not as strong in predicting hospitalizations as various physical health measures (e.g., self-reported physical health, physical comorbidity) (69, 77). Regarding ED use, U.S. studies suggest that mental health disorders are a key driver of ED use, regardless of insurance coverage. Capp et al.’s (78) large U.S. study with over 66 million annual visits found that ED visits increased by 8.6% from 2006 to 2011, yet ED visits by adults primarily for mental health disorders increased by 20.5%. Mental health disorders have also been found to be a significant factor accounting for non-urgent ED use (79). While our study did not find that self-perceived mental health was associated with ED use, this may be due to differences across studies in the mental health measure used – e.g., self-reported mental health (our measure) is dimensionally different than objective measures of mental illness (80) and is not recommended as a substitute/proxy for mental diagnoses (75, 81).
Living alone influenced hospitalizations but not ED use, with living alone associated with higher hospitalizations in our study. Results are conflicting in studies that have examined this issue – e.g., Shaw et al. (82) and Cafferata (83) found that living alone was associated with higher use of hospital services, Manski et al. (84) found no difference in hospital use among those living alone versus with someone, and a systematic review of 126 studies found that weaker social relationships were associated with increased hospital re-admissions and longer hospital stays (85). Inconsistent findings may reflect differences in measuring and/or equating constructs – e.g., social isolation and loneliness are not the same entity (86) and living alone does not necessarily indicate social isolation (87). However, it is plausible that social relationships impact acute care service use given reported links between social isolation/loneliness and poor health (88, 89) and studies showing that social isolation/loneliness predicts ED use (79, 90–94).