Summary
We found that patients with higher continuity based on registration with their GP’s practice longer than 5 years had significantly lower odds of urgent hospital admissions (9%-21% lower) and lower hospital costs (17%-28% lower) compared with those registered for 0 to 5 years, after adjusting for age, sex, number of chronic conditions, household income, and migration background. Although higher continuity based on density of GP contacts was not associated with urgent admissions, it was associated with relative reductions in hospital costs (6%-7%). These findings highlight the potential value of sustained GP-patient relationships in reducing future hospital health care use and costs in the Netherlands.
Strengths and Limitations
To the best of our knowledge, this is the first study to examine the association between continuity in general practice—assessed with multiple conceptually distinct measures of continuity—and both hospital use and costs within the same analysis. We studied continuity of general practice care from different perspectives: the practice (using duration of registration as a proxy for GP-patient continuity) and the patient (using an established continuity index as proxy for density of GP-patient contacts). Use of these measures allowed us to capture continuity at different levels within contemporary primary care. In previous studies, we used multiple indices to calculate density of GP contacts, which showed associations similar to those seen with the Herfindahl-Hirschman index.9,32 The study reported here was based on longitudinal real-life health care data of 100,450 patients from 48 general practices in and around Amsterdam and had similar continuity levels compared with those in practices in other studies.33,34 We therefore consider our results representative and generalizable, especially for urban Dutch general practices.
Some limitations of our study should be acknowledged. First, we applied 2 major inclusion criteria: (1) patients had to have contacted their practice at least 5 times, including at least 2 contacts with a GP, to enable calculation of GP-contact density, and (2) patients had to remain registered at a specific practice through December 31, 2018, to ensure they were not receiving primary care elsewhere. As a result, patients who avoided, declined, or did not require care—and thus had no GP contacts—were excluded. Consequently, we were unable to assess the association between zero continuity and hospital admissions or costs.
Second, these inclusion criteria may have acted as a collider, particularly affecting recently registered patients. Although examination of the pre-linkage data set suggests that the group registered 0 to 5 years was not predominantly composed of recent registrants (Supplemental Figure 1), residual cohort construction effects cannot be fully excluded.
Third, although we successfully matched 85.7% of patients to data from Statistics Netherlands using date of birth, sex, and postal code, some patients may have been inadvertently excluded. This is particularly likely for individuals with missing or generic birth dates (eg, January 1 or July 1), which are often assigned to people with a first-generation migration background. As the achieved match rate is generally considered acceptable, however, selection bias is unlikely.35
Fourth, age is inherently correlated with length of continuity, which may introduce collinearity and complicate interpretation of their independent associations. Although analyses were adjusted for age, residual collinearity cannot be fully excluded. Furthermore, even though we adjusted for the number of chronic conditions, residual confounding by illness severity may persist. Other unmeasured factors, such as patient residential mobility or physician turnover, may have influenced observed continuity patterns but could not be assessed in this study. Missing data on outcomes hospital costs or admissions are unlikely, because both are routinely reported to Statistics Netherlands by health insurers and hospitals.31
It is important to note that our study focused on hospital costs. Consequently, we are unable to draw conclusions about the relationship between continuity of care and costs that extend beyond hospital care. Regarding hospital admissions, our data included only admissions to hospitals within the Netherlands. We do not have access to data on admissions occurring abroad.
Comparison With Existing Literature
More than 30 years ago, Hjortdahl36 suggested that it takes at least 5 years to create an “extensive knowledge base” between GP and patient. Although a lot has changed since, our study shows a similar trend, as patients who were registered longer than 5 years had lower hospital costs. This suggests that longer enlistment may contribute to more efficient care, potentially through accumulated knowledge and increased trust. Additionally, we found that higher density of contacts was associated with cost reductions, reinforcing the value of seeing the same GP. We acknowledge, however, that these observed associations may not be fully attributed to continuity alone. Patients with a higher risk of hospital admissions and costs may be more likely to change GP or general practice for various reasons, ranging from relocating closer to caregivers to being dissatisfied with their previous GP.
Although many studies have examined the relationship between continuity of care and health care use or costs, they have varied widely in design, continuity measures, populations, and outcomes. This heterogeneity, as described in a review by Bazemore et al in 2023,20 complicates direct comparisons.
To our knowledge, only a single study has been published on the association between continuity and health care use using a Dutch general practice population.37 That study found that patients registered less than 1 year had a higher probability of receiving an antibiotic prescription as a proxy for health care use, although the study did not evaluate broader outcomes including hospital admissions or costs.
A study from the United Kingdom using the Usual Provider of Care index found that a 0.2-point increase in continuity could reduce avoidable admissions by 6.2%.15 Continuity was measured over a 2-year period and admissions were limited to a predefined list of 22 conditions, however. In contrast, our study used a broader population and focused on all urgent admissions, which may be less influenced by continuity because of their acute nature. We found no association between contact density and urgent hospital admissions. Perhaps, patients with medical reasons for more frequent visits have a higher contact density, potentially attenuating the protective effect of continuity. In addition, urgent admissions may be related to accidents or acute events, which may be independent of GP continuity.
