What Interventions Work to Reduce Cost Barriers to Primary Healthcare in High-Income Countries? A Systematic Review

High-income countries like Aotearoa New Zealand are grappling with inequitable access to healthcare services. Out-of-pocket payments can lead to the reduced use of appropriate healthcare services, poorer health outcomes, and catastrophic health expenses. To advance our knowledge, this systematic review asks, “What interventions aim to reduce cost barriers for health users when accessing primary healthcare in high-income countries?” The search strategy comprised three bibliographic databases (Dimensions, Embase, and Medline Web of Science). Two authors selected studies for inclusion; discrepancies were resolved by a third reviewer. All articles published in English from 2000 to May 2022 and that reported on outcomes of interventions that aimed to reduce cost barriers for health users to access primary healthcare in high-income countries were eligible for inclusion. Two blinded authors independently assessed article quality using the Critical Appraisal Skills Program. Relevant data were extracted and analyzed in a narrative synthesis. Forty-three publications involving 18,861,890 participants and 6831 practices (or physicians) met the inclusion criteria. Interventions reported in the literature included removing out-of-pocket costs, implementing nonprofit organizations and community programs, additional workforce, and alternative payment methods. Interventions that involved eliminating or reducing out-of-pocket costs substantially increased healthcare utilization. Where reported, initiatives generally found financial savings at the system level. Health system initiatives generally, but not consistently, were associated with improved access to healthcare services.


Introduction
Primary healthcare constitutes an integral part of the health system and is widely regarded as the most inclusive and cost-effective strategy to achieve universal health coverage [1].As it is often the first point of contact with the health system and a gatekeeper to secondary services, access to primary healthcare is a critical factor in the performance of the whole health system [2].Access to primary healthcare refers to the attributes of the service provided, the characteristics of health professionals, and the resources used to enable a population to seek and obtain care [2].It is suggested by the World Health Organization and other health agencies that a primary healthcare system that is robust and accessible is paramount to reducing healthcare inequities, improving system efficiency, and achieving better patient experience and quality of treatment [1,3,4].
Many high-income countries, including the United Kingdom, Italy, Australia, Canada, and Aotearoa New Zealand, employ a capitation formula to fund primary healthcare and/or secondary services.This formula accounts for the size and characteristics of a population, such as age and sex, to estimate the funding needed to match the community's predicted healthcare needs [5].However, these formulae are primarily modelled on historical healthcare utilization and insufficiently account for the issues experienced through and between heterogeneous population groups, such as deprivation and ethnicity, which often reinforce health disparities and inequities [2,6].In health systems like those in Australia and Aotearoa New Zealand, consultation costs that exceed the capitation coverage are paid out of pocket by the health user or guardian.International evidence reports that relying on out-of-pocket healthcare payments is inequitable and inefficient [7].The arguments for copayments are that they promote cost-conscious service utilization and may encourage healthier lifestyle behaviours [8].Nonetheless, when healthcare is appropriate, copayments can delay treatment, resulting in health status deterioration and increased financial burden for the overall system, for example, higher rates of avoidable hospital admission [7,9].A large-scale, multiyear experience found that cost sharing (i.e., costs are shared by insurance and paid out of pocket by a user) reduced "inappropriate or unnecessary" medical care but also, subsequently, "appropriate or necessary" healthcare services [9].Furthermore, out-of-pocket costs disproportionately affect those of lower socioeconomic status and exacerbate poverty [10].It is argued that out-of-pocket costs for primary healthcare services are a cause of or, at the very least, an aggravator of poverty [11].
In October 2015, the United Nations adopted the Sustainable Development Goals (SDGs) to stimulate action over the next fifteen years in areas of critical significance for humanity and the planet [12].Of importance, SDG3 (Target 3.8) set the objective for Member States to achieve universal health coverage, including protection against financial risk and the accessibility to medicines and vaccines for all [13].Despite the commitment from Member States, primary healthcare systems worldwide still need to be developed, as they fail to provide high-quality, inclusive, affordable services for all populations.
It is more necessary than ever to address the inaccessibility and unaffordability of primary healthcare services in high-income countries.The consequences of failing to invest in primary care were demonstrated in the COVID-19 pandemic, which, in turn, brought a renewed focus on a primary healthcare system that is robust and affordable.Various strategies, with differing levels of success, have been implemented internationally to reduce financial barriers to the health user when accessing primary healthcare.This has led to the implementation of a diverse range of programs that intend to improve access to healthcare services but more often create confusion for the health user and clutter the healthcare space.Thus, we conducted a systematic literature review to synthesize evidence of interventions addressing cost barriers for health users when accessing primary healthcare in high-income countries.From this, we aimed to comprehensively review successful strategies that may benefit other high-income countries.

Materials and Methods
This systematic review was conducted and reported following the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) Guidelines.Given the heterogeneity of the study designs included in this review, no meta-analysis was undertaken.Instead, we conducted a narrative synthesis and applied a quality appraisal using the Critical Appraisal Skills Program (CASP) checklists.No protocol was registered for this review.

Search Strategy and Retrieval of Studies
Searches of databases using a combination of key terms were trialed in April 2022.The purpose of this trial was to provide evidence of which terms offered the most comprehensive retrieval of the literature and informed the selection of databases used within the search strategy.Three electronic bibliographic databases were selected as a result of the trialing process: Medline Web of Science, EMBASE, and Dimensions.A preliminary search found that few publications included relevant terms within the title or abstract.Therefore, the search for keywords included the full text of the article to allow for a substantial collation of evidence to undergo eligibility screening.
Limits applied to the search were tailored to each database.For example, Dimensions allowed countries to be selected to provide publications from high-income countries.
However, not all high-income countries, as defined by World Bank Data [14], were available to choose from.Therefore, we accounted for this by including "NOT low/medium income countr*".This strategy was also applied to the Web of Science and EMBASE.Furthermore, all databases allowed us to limit our search to English-only publications and exclude specific research studies, such as literature reviews, study protocols, and presentations.
The search of the literature using the three electronic databases and predefined search terms was conducted in April 2022.Research keywords are outlined in Tables 1 and 2. Search terms from the combined databases were imported into Zotero, a bibliographic management program, and duplicate citations were removed using Zotero's duplicate identification tool [15].Duplicates that were missed by Zotero were highlighted by Rayaan's duplication identification tool later in the eligibility screening.An additional search of reference lists of single studies and literature reviews that were deemed relevant but that did not fit the eligibility criteria was undertaken.

Inclusion and Exclusion Criteria
The eligibility criteria of this systematic review included the following: 1.
The article reported on the outcomes of interventions; 2.
Interventions aimed to reduce cost barriers in primary healthcare settings; 3.
The study included a defined population residing in a high-income country, as defined by the World Bank; 4.
The article was published in English between January 2000 and April 2022.
Peer-reviewed articles for all study designs, including observational and experimental, were eligible for inclusion.Exclusion criteria included articles published before January 2000, non-English-language studies, and those on low-to medium-income countries.The exclusion of low-to medium-income countries was conducted by omitting any articles that mentioned "low-income country(/ies)" or "medium-income country(/ies)" in their title or abstract.No specific countries were individually named to be excluded.

Study Selection
The remaining publications were exported from Zotero into Rayaan, an online tool designed to facilitate the screening and selection of studies [16].Two reviewers (BY and NM) independently undertook an initial screening by title and abstract.A third reviewer (FMcK or MJ) adjudicated conflicting records to ensure uniformity.If the title and/or abstract of a potentially relevant citation did not provide sufficient information to determine inclusion, the report proceeded to the full-text review, in which two reviewers (BY and NM, FMcK, or MJ) independently assessed the article's manuscript for eligibility.

Data Extraction
Data from articles were extracted by one reviewer (BY) and checked by another (NM, FMcK, or MJ), with any discrepancies resolved through discussion.The following information from quantitative and qualitative studies was extracted using a template in Microsoft Excel: (1) publication details (i.e., author, year, and country); (2) methods (i.e., population, study design, and data); (3) intervention and comparator; (4) results and outcomes.

Quality of Evidence
Two reviewers critically appraised all included publications using the CASP checklists (see Supplementary Tables S1-S4).In most studies, reviewers agreed on the articles' appraisal and quality assessment determinations.Where discrepancies appeared, these were resolved by the resolution of one experienced reviewer (MJ).As recommended by the CASP checklist, the items listed were not scored using a point system.Instead, items were recorded using "yes", "no" or "not applicable" [N/A] responses.The accumulation of these responses determined the overall appraisal of the publication as "satisfactory" or included with "caution" (see Tables 3-8).

Synthesis Process
Given the heterogeneity of study designs, we combined the results in a narrative synthesis.Study findings were tabulated into categorized intervention types (i.e., total removal of out-of-pocket payments), then grouped into outcome categories considered relevant, for example:

•
Healthcare utilization: rates of physician visits.

•
Cost savings: changes in out-of-pocket costs and expenditures per patient per practice.• Accessibility: the likelihood of being accepted as a new patient by a healthcare provider and reported barriers experienced by a patient.
Interventions with more than one component (i.e., the Affordable Care Act [ACA] expansion with eligible/non-eligible dual beneficiaries) were categorized according to the primary component emphasized by the authors.
A subgroup analysis was conducted to synthesize evidence of interventions from high-income countries that employed a capitation-style funding arrangement for primary healthcare service providers.This allowed for an examination of the cost-reducing methods most complementary to the health and disability system in Aotearoa New Zealand and their outlined levels of success.

Literature Search and Review Process
Based on the publications' titles and abstracts, 89 articles were retrieved for full-text review from 18,111 potentially relevant citations (Figure 1).The retrieved full-text articles were assessed against the eligibility criteria, and 60 were excluded.The reference lists of eligible full-text articles were scanned for relevant publications, and 20 studies were further included.Following a comprehensive three-phase screening, six publications were excluded due to insufficient information, and one study was a nondisclosed literature review.This brought the total to 43 included articles in this review.

Characteristics of Included Publications
The characteristics of the included articles are presented in Tables 3-8.Nearly half (48.8%) of all articles were published between 2015 and 2019.Thirty-one (72.1%) publications were located in the United States, followed by five (11.6%) in Canada and two (4.7%) each in Ireland and Japan.One study (2.3%) was based in each of Aotearoa New Zealand, Australia, and Sweden.Most interventions were implemented at the practice level, including the implementation of nonprofit organizations and community programs (30.2%), alternative payment methods (14.0%), total removal of out-of-pocket costs (11.6%), and additional workforce (4.7%).Other system-level interventions included the ACA in the United States (32.6%) and reforms or initiatives in Sweden and Canada (7.0%).Some interventions targeted specific population groups, such as low-income earners (federal poverty level [FPL] < 200%) (10.9%), individuals with preexisting health conditions (10.9%), children aged under 12 years (6.5%), or older people aged above 65 years (8.8%).A few interventions targeted two population groups concurrently (e.g., low-income earners and those with preexisting health conditions).More than half of the outcomes reported were changes in healthcare utilization (58.1%), followed by cost savings (18.6%), accessibility (14.0%), and medication adherence (9.3%).

Quality of the Evidence
The results of the CASP checklists are summarized in Supplementary Tables S1-S4.Most studies were considered at low risk of bias and were deemed to satisfy the quality assessment.No studies were excluded based on the level of quality appraisal.The results from a few articles were included but interpreted cautiously.

Total Removal of Out-of-Pocket Costs
All five publications that implemented some form of out-of-pocket removal reported increased healthcare utilization and/or adherence to appropriately prescribed medicines [17][18][19][20][21].Most studies targeted children under 12 [17,19,20] or older persons above 65 years [18].Two studies employed interventions in the form of total medical cards [19] and valuebased insurance designs [20].Other articles implemented the complete removal of user charges [17,18,21].

Additional Workforce
Two publications investigated the effect of increasing the workforce to reduce cost barriers experienced by patients in primary healthcare services.One investigation reported that Medicare costs per patient for practices that did not employ nurse practitioners are USD 445 higher than for healthcare services that did employ nurse practitioners

Quality of the Evidence
The results of the CASP checklists are summarized in Supplementary Tables S1-S4.Most studies were considered at low risk of bias and were deemed to satisfy the quality assessment.No studies were excluded based on the level of quality appraisal.The results from a few articles were included but interpreted cautiously.All five publications that implemented some form of out-of-pocket removal reported increased healthcare utilization and/or adherence to appropriately prescribed medicines [17][18][19][20][21].Most studies targeted children under 12 [17,19,20] or older persons above 65 years [18].Two studies employed interventions in the form of total medical cards [19] and value-based insurance designs [20].Other articles implemented the complete removal of user charges [17,18,21].

Additional Workforce
Two publications investigated the effect of increasing the workforce to reduce cost barriers experienced by patients in primary healthcare services.One investigation reported that Medicare costs per patient for practices that did not employ nurse practitioners are USD 445 higher than for healthcare services that did employ nurse practitioners [22].However, the study's findings did not reach conventional levels of statistical significance.The other study found intervention subjects were more likely to have primary care contact when paired with a health promotion advocate than those who were not paired (51.2% vs. 13.8%,p < 0.001) [23].However, the study appraisal of this investigation was included in this review with caution.

Alternative Payment Methods
Six articles assessed alternative payment methods as an intervention to combat cost barriers to healthcare services.Two investigations reported no significant difference in health utilization and accessibility between intervention and comparison groups [24,25].One study targeted low-income earners (<182% FPL) and found that insured enrollees were less likely to delay care due to appointment costs than uninsured enrollees (21.3% vs. 78.5%)[26].Another study targeted older people (aged 64 to 75 years) and reported that out-of-pocket spending was significantly lower than those who were non-eligible for the intervention, aged below 64 years [27].One investigation examined the reduction of copayments on pharmaceutical products and found that a lower copayment increased medication adherence [28].Contrastingly, one study found an increase in pharmaceutical copayments was related to decreased medication possession ratios and increased rates of product discontinuation [29].

Reforms and Initiatives
Two out of three investigations reported small or unimproved outcomes.One study reported that the transformation from a needs-weighted capitation formula with ageand area-specific proxies compared to a fee-for-service formula increased doctor visits but observed smaller increases in visits in those with more significant healthcare needs, such as men living in disadvantaged areas [30].Another investigation reported minimal increases in primary healthcare visits and no substantial changes in average expenditures than the comparison clinics [31].One analysis investigated a "Mandatory Universal Drug Prescription" in Quebec, Canada, and found pharmaceutical use increased by thirteen per cent relative to other provinces [32].

The Affordable Care Act Expansions
Fourteen studies investigated the impact of the U.S. ACA on mitigating cost barriers to healthcare services [33][34][35][36][37][38][39][40][41][42][43][44][45][46].Two investigations examined the effects of Medicare's Part D Prescription Benefit, which targeted those with low incomes and the elderly aged above 65 years [33,34].Both studies found the benefit of reduced medication expenditures and increased pharmaceutical use.One article reported an increase in out-of-pocket spending among those in the subsidized marketplace coverage (ACA) compared to employersponsored insurance (adjusted difference in difference [aDiD]: 9.7 percentage points) [35].One investigation found that healthcare users were less likely to report barriers to accessing healthcare services after the ACA implementation than in the prior year [36].Another publication used a stock-and-flow projection model and reported access to healthcare services would improve by about 20.0% under the expansion.However, subsequently, it also reported the availability of physician appointments would decrease by 13.0 to 19.0% [37].Six of eight articles reported increased physician visits and screening uptake [38][39][40][41][42][43].Of the two studies that did not, one investigation reported visit rates to primary physicians declined more for dual beneficiaries (who received both Medicaid and Medicare benefits) after the implementation of the ACA than the year before implementation (DiD: −0.37 [95%CI: −0.43 to 0.32] visits per 100 beneficiaries in 2013 to 2014 vs. 2012, p < 0.001) [44].Another investigation reported mixed findings in healthcare utilization between patient populations.Overall, rates of primary healthcare visits did not increase from pre-to post-ACA in the expansion and non-expansion states for diabetic and nondiabetic patients.However, among patients with prediabetes, primary healthcare visit rates in the expansion states increased by 14 per cent (RR: 1.14; 95%CI: 1.08 to 1.19) [45].One study reported that those who gained and/or maintained Medicaid expansion insurance displayed long-term primary healthcare use patterns similar to those continuously insured [46].

Implementation of Not-for-Profit Organizations and Community-Based Programs
Three studies reported reduced out-of-pocket charges or improved organizational cost savings after introducing some form of a not-for-profit entity.This included interventions such as a clinic operated by nurses [47], community-governed organizations [48], and alternative models of primary healthcare [49].One study that investigated the impact of a "Community-based Outreach Agency" that employed a multitouch outreach model to foster long-term access to healthcare reported that low-income Latino patients were 60.0% less likely to experience a barrier in accessing primary healthcare, including not being able to afford to pay for a consultation (aOR = 0.4; 95%CI: 0.30 to 0.70) [50].However, this investigation was outlined and included with caution.Three studies reported that access to services and healthcare utilization improved when financial viability was underpinned by capitation-style funding or enhanced fee-for-service models that included payment incentives and were not entirely reliant on user charges [51][52][53].Three investigations that reported some form of community healthcare provider found increased visitation and appointment rates compared to the non-exposure group [54][55][56].One study that investigated Quebec's Family Medicine Group, a team-based model of care that remained fee-for-service but with additional fixed payments and afterhour availability, found rates of general practitioner visits decreased by 0.45 (p < 0.001), and thus, lowered out-ofpocket spending by CAD 11.00 per patient, per year.The investigation further reported finding no evidence that the reduced rate of physician visits was driven by substituting fewer, longer consultations for shorter ones [57].One article that investigated the effects of a "Case Management Community Health Program", which involved developing a preventive care regimen tailored to the specific needs of a patient, reported that program participation was statistically associated with an increase in primary healthcare visits from an average of 4.13 to 10.82 (p < 0.001) [58].One investigation that offered enhanced fee-forservice capitation payments through a "Primary healthcare Case Management Program and Performance Incentives" for professionals reported a decline in avoidable hospitalizations and emergency department visits by 16.8% and 5%, respectively [59].

Subgroup Analysis of High-Income Countries with Capitation Formulae
Nine publications (20.9%) were based on high-income countries that employed capitation as a primary funding arrangement for healthcare providers.Over half of the articles (55.6%) involved the "implementation of not-for-profit organizations or community programs" followed by the "removal of out-of-pocket costs" (33.3%), and "initiatives or reforms" (22.2%) from Canada and Sweden.Most outcomes reported comprised healthcare utilization (33.3%), followed by equal parts medication adherence and healthcare accessibility (22.2%), and one study reported on cost savings (11.1%).All publications that removed out-of-pocket costs reported favourable results, with increased physician visits and medication adherence [19,21,59].Studies that investigated the impact of initiatives or reforms provided mixed results.One study reported no evidence that a reform benefitted those with more significant healthcare needs [30].Another study reported a 13.0% difference in pharmaceutical use between Quebec and the rest of Canada when a Mandatory Universal Prescription Drug Program was introduced in Quebec [32].All studies investigating some form of a not-for-profit organization reported reduced out-of-pocket charges and increased physician visits than for-profit organizations [48,57].A variation of primary healthcare models reported that access to healthcare services, screening uptake, and out-of-pocket costs were improved when financial viability was underpinned by capitation rather than total reliance on fee-for-service models [49,52,53].

Healthcare utilization
The mean number of physician visits increased for all groups from pre-to post-intervention (56% vs. 65%, a relative increase of 1.17).However, men living in disadvantaged areas had a significantly smaller increase than their reference groups.
Only two time points were measured.Nonrespondents were stated to be overrepresented in social and economically disadvantaged groups.There is the possibility of confounding variables.

Discussion
To our knowledge, this is the first systematic review of the international literature to examine interventions implemented to reduce cost barriers to primary healthcare in high-income countries.Through this synthesis of evidence, we identified the type of interventions most commonly employed to reduce cost barriers in primary healthcare and which outcomes were most affected.This review followed a rigorous methodology and comprised 43 peer-reviewed articles which covered six broad groups of interventions.In total, most publications presented in this review found statistically significant improvements, whilst a few reported mixed or nonstatistically significant findings in their primary outcomes.
From the synthesis of the literature, several key findings emerged.The most consistent was that the complete removal of out-of-pocket costs was associated with significant improvements in doctor visitation rates and medication possession ratios.Most publications in this intervention group targeted specified populations, such as children and/or older adults.Therefore, the generalizability of the literature findings and, thus, the feasibility of this intervention to other population cohorts remains unclear.Likewise, interventions that lowered out-of-pocket costs through alternative payment methods, such as cost sharing, generally reported improved medication adherence and access to primary healthcare outcomes.Studies that investigated the effects of increasing the healthcare workforce reported an increased uptake of follow-up appointments and lower Medicaid expenditure per person per practice.Health system initiatives generally, but not consistently, were associated with improved access to healthcare services.Of interest, Sweden's transition from a needs-weighted capitation formula with age-and area-specific proxies to fee-for-service funding arrangements found significantly smaller increases in the number of visits for those with more significant healthcare needs than those who were healthy.This study finding demonstrates that the transition to a healthcare system that relies predominantly on out-ofpocket payments of health users does not benefit those with greater healthcare needs to the same extent as those with lesser needs, exacerbating health inequities and, consequently, worse healthcare outcomes.In contrast, Quebec's Mandatory Universal Prescription Drug Program provided public medicine coverage for those who do not have private plans and found an increase in medication use and practitioner visits.Most articles published in the United States investigated the impact of the ACA and found, on average, that expansion states showed improved outcomes relative to non-expansion states or found that physician visitation rates were higher postimplementation of the ACA than a year prior.
This review found that capitation-style funding increased access to healthcare services and screening uptakes and reduced out-of-pocket costs for users compared with healthcare providers with complete reliance on fee-for-service funding arrangements.Although some capitation funding arrangements still required out-of-pocket gap payments for healthcare services, this is, comparatively, much lower than fee-for-service arrangements in which users pay for the total care charge.This full charge substantially deters those from seeking healthcare, contributing to a patient's health status deterioration, and is more likely to significantly impact those who are less financially stable [10,11].Service-level interventions, such as not-for-profit organizations and community-based programs, reported favourable results in reduced out-of-pocket costs and increased physician visitation rates compared to for-profit organizations.As highlighted in an Aotearoa New Zealand study included in this review [45], not-for-profit organizations and community-based programs were more likely to provide health services at reduced costs or zero charges.This limited or eliminated the financial barrier experienced when accessing healthcare providers and, more often, resulted in an increased rate of physician consultations than for-profit organizations.This review found the total removal of out-of-pocket costs for service users demonstrated increased visits to a physician and improved medication adherence.This finding reflects the simplicity of this intervention and its effects.Entirely removing out-of-pocket costs and, thus, eliminating the financial barrier in accessing primary services will, in return, increase patient healthcare utilization and medicine adherence.However, it is important that access to high-quality primary healthcare is maintained.The provision of free healthcare appointments could lead to increased demand, and without adequate investment in staffing and service funding, this could result in a shortage of physician appointments, creating another barrier to access.For instance, a stock-and-flow project model included in this review found that while the ACA expansion increased healthcare access, it also led to a decrease in the availability of physician appointments [37].Our review reported the possible effectiveness of increasing the workforce, which led to improved cost savings and healthcare utilization for the patient [22,23].A hybrid model that combines a variety of interventions, such as the elimination of out-of-pocket costs and the increased utilization of nurse practitioners, may be worth considering to improve access to primary healthcare.
Cost barriers to accessing primary healthcare services ingrain health inequity at the system level.Out-of-pocket costs in healthcare can be crippling to the financial stability of an individual and their household [7,10,11].More often, those with lower incomes may choose to forgo healthcare, contributing to a deterioration of health status [10,11].This worsening increases the likelihood of experiencing poverty by reducing one's ability to work and, consequently, declining wages associated with paid employment [60].This cycle has been demonstrated globally, as those who cannot improve their financial capacity to afford healthcare due to poor health status fall deeper into poverty-related circumstances [60].Furthermore, the repercussions of out-of-pocket costs associated with healthcare can transcend to affect other areas of living.For example, as healthcare expenditures increase, this reduces the amount of disposable income available to spend in different areas, such as food, transport, accommodation, or entertainment [60].The primary healthcare system in Aotearoa New Zealand is largely funded through capitation-based arrangements for general practices, supplemented by user copayments [5].The shift from fee-for-service towards universal-weighted capitation was introduced through a set of primary healthcare reforms aimed at lowering patient copayments and promoting population health [61,62].The capitation funding formulae supplied to healthcare providers are based on historical utilization rates of general practices and the age and sex of patients enrolled [63].Over the past decade, many organizations have raised concern that the formulae fail to consider a community's level of deprivation and ethnicity and question whether the formulae exacerbate existing inequities or act to address them [61,63,64].In this review, few studies were based in high-income countries that employed capitation as a primary funding scheme for healthcare providers, similar to Aotearoa New Zealand.Therefore, this limits any generalizability of findings and the implications of interventions if implemented in Aotearoa New Zealand's health and disability system.

Strengths and Limitations
As a strength, this literature review explored real-world interventions in high-income countries and identified six interventions to reduce cost barriers to primary healthcare for all populations.Furthermore, this review exclusively analyzed high-income countries that employed capitation as a primary funding source for healthcare providers in a subgroup analysis to investigate cost-reducing methods most complementary to the health and disability system in Aotearoa New Zealand.Finally, this review demonstrates that the complete removal of out-of-pocket costs to healthcare eliminates financial barriers experienced by healthcare users and provides consistent and favourable results.Likewise, reducing out-of-pocket user charges through cost-sharing methods also provides beneficial outcomes, but less consistently.
This review does have limitations that should be considered carefully.First, we relied entirely on electronic databases to search for relevant citations and included only English publications.It is possible other relevant studies could have been eligible for this review if we were to include articles published other than in the English language or used broader forms of search engines, such as grey material and presentation notes.Second, some interventions targeted specific populations, e.g., the complete removal of out-of-pocket costs targeting children or older people.The impact of such interventions on a population level may not be the same as that on specific groups.Third, there is concern about whether increased health utilization is an appropriate measure of improvement in primary healthcare access.Various international investigations have raised awareness that the quantity of healthcare services is not always a substitute for quality [65].As addressed in our review, it is possible that patients are able to attend more healthcare services after the intervention, but the quality of care received may be reduced, predisposing them to worse patient health outcomes.For example, as healthcare services become more affordable, the demand and uptake of such services from patients increases.To meet this increase in demand, physicians must be able to fit a surplus of consultations in the same number of working hours, often with inadequate funding to do so.Therefore, appointments become shorter, and the relationship between practitioner and client may suffer.To mitigate this effect, it is worth considering a hybrid model that combines a variety of interventions, such as investment in staffing levels and the removal of out-of-pocket costs to improve access to primary healthcare.Lastly, financial barriers to primary healthcare are limited not only to out-of-pocket costs associated with the healthcare service but also to other payments, such as transportation, paying caregivers for dependents, and opportunity costs, such as time off work [5].Other barriers to primary healthcare can include but are not limited to gender-based and/or cultural constraints, lack of health literacy, and poor infrastructure support [66,67].Therefore, we emphasize the importance of a multidimensional view of healthcare access, as proposed by Levesque et al. [68].This framework considers the socioeconomic determinants of individuals to identify, seek, reach, obtain, and engage in primary healthcare services [69].

Conclusions
Many international efforts have been implemented to reduce cost barriers to primary healthcare in high-income countries, with differing levels of success.In this review, the complete removal or lowering of out-of-pocket costs through direct or alternative payment payments, such as cost sharing, significantly increased healthcare use and medication adherence.Universal healthcare with financial risk protection is a core objective of the Sustainable Development Goals.The persistence of out-of-pocket costs in primary healthcare works against commitments outlined by Member States and disproportionately affects those most vulnerable, predisposing them to catastrophic healthcare expenditures and income poverty.A range of initiatives to improve access to primary healthcare could address these problems to impact health equity and reduce overall health system costs.

Figure 1 .
Figure 1.Search and screening flowchart: PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) summarizing the identified literature focused on interventions to reduce cost barriers to primary healthcare in high-income countries, 2000-2022.

Figure 1 .
Figure 1.Search and screening flowchart: PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) summarizing the identified literature focused on interventions to reduce cost barriers to primary healthcare in high-income countries, 2000-2022.

3. 4 .
Interventions to Reduce Cost Barriers to Primary Healthcare Services 3.4.1.Total Removal of Out-of-Pocket Costs Abbreviation: NHI: National Health Insurance; FFS: fee-for-service; RCT: randomized controlled trial; OR: odds ratio; 95%CI: 95% confidence interval.SAT: The quality appraisal of the study reached satisfactory levels as determined by the CASP checklist.

Table 1 .
The search strategy of the Web of Science and EMBASE databases.

Table 2 .
The search strategy of the Dimensions database.

Table 3 .
Study characteristics of included publications grouped by "total removal of out-of-pocket costs".

Table 4 .
Study characteristics of included publications grouped by "additional workforce".
SATAbbreviations: NPs: nurse practitioners; CAUT: no studies were excluded on the basis of the level of quality appraisal.However, as determined the CASP checklist, the article was included with caution.

Table 5 .
Study characteristics of included publications grouped by "alternative payment methods".

Table 6 .
Study characteristics of included publications grouped by "reforms and initiatives".

Table 7 .
Study characteristics of included publications grouped by "the Affordable Care Act expansions".

Table 8 .
Study characteristics of included publications grouped by "implementation of not-for-profit organizations and community programs."