Impact of vertical integration on patients’ use of hospital services in England: an analysis of activity data

Background Debate surrounding the organisation and sustainability of primary care in England highlights the desirability of a more integrated approach to patient care across all settings. One such approach is ‘vertical integration’, where a provider of specialist care, such as a hospital, also runs general practices. Aim To quantify the impact of vertical integration on hospital use in England. Design & setting Analysis of activity data for NHS hospitals in England between April 2013 and February 2020. Method Analysis of NHS England data on hospital activity, which looked at the following seven outcome measures: accident and emergency (A&E) department attendances; outpatient attendances; total inpatient admissions; inpatient admissions for ambulatory care sensitive conditions; emergency admissions; emergency readmissions; and length of stay. Rates of hospital use by patients of vertically integrated practices and controls were compared, before and after the former were vertically integrated. Results In the 2 years after a GP practice changes, for the population registered at that practice, compared with controls, vertical integration is associated with modest reductions in rates of A&E attendances (2% reduction [incidence rate ratio {IRR} 0.98, 95% confidence interval {CI} = 0.96 to 0.99, P<0.0001]), outpatient attendances (1% reduction [IRR 0.99, 95% CI = 0.99 to 1.00, P = 0.0061]), emergency inpatient admissions (3% reduction [IRR 0.97, 95% CI = 0.95 to 0.99, P = 0.0062]), and emergency readmissions within 30 days (5% reduction [IRR 0.95, 95% CI = 0.91 to 1.00, P = 0.039]), with no impact on length of stay, overall inpatient admissions, or inpatient admissions for ambulatory care sensitive conditions. Conclusion Vertical integration is associated with modest reductions in use of some hospital services and no change in others.


Introduction
At the founding of the NHS in the UK in 1948, general practices, providers of primary medical care, were kept organisationally separate from hospitals and other providers of secondary care.This arrangement lasted for decades but since 2015, some general practices have started to be run by secondary care provider organisations, which are known as 'trusts' in the NHS in England.This is a form of vertical integration of health care.2][3][4] Vertical integration has emerged in response to local initiative rather than national mandate.Davies et al identified in England at the end of March 2021 a total of 85 general practices (operating from 116 sites) being run by 26 trusts. 5These represent one in 80 general practices and one in nine trusts.
The most important driver for trusts to run general practices has been found to be to safeguard continued delivery of care local to where patients live and thereby enable better management of how patients use hospital services. 6,7][10][11] Vertical integration creates opportunities for developing patient services in primary care settings and better integrating them with secondary care to achieve improved patient outcomes and patient experiences of health care. 6,7ustaining primary care, alongside growing patient demand and workforce constraints, is a matter of increasing concern. 12Better integration and coordination of primary and secondary care services are among suggestions to address it. 14][15] A study of vertical integration between an acute hospital and 10 general practices in the West Midlands of England, found that it was associated with a reduced rate of unplanned hospital admissions and readmissions, and corresponding opportunities for reductions in hospital costs. 16In 2022, the Secretary of State for Health and Social Care in England stated interest in encouraging vertical integration. 17,18e report here a study across all instances of vertical integration in the NHS in England up to 31 March 2021 to determine the impact of vertical integration on patients' use of hospital services.This work was part of a larger, mixed-methods project to evaluate the impact of vertical integration on efficiency outcomes and patient experience; a detailed report of which is published elsewhere. 19

Method
We compared practices that underwent vertical integration with trusts with control practices in England using data from April 2013-February 2020 on patients' use of secondary care.

Outcomes
We used person-level Hospital Episode Statistics (HES) activity data from NHS Digital (which has now merged with NHS England), 20 accessed under a Data Sharing Agreement, to evaluate the impact of vertical integration for seven outcome measures of secondary care utilisation, as shown in Table 1.

Table 1 Secondary care utilisation measures
Outcome Details

A&E attendances
All A&E attendances at all types of emergency care departments and providers were included.For financial year 2019-2020 we used HES A&E data rather than the new Emergency Care Data Set, to maintain consistency across the whole analysis timeframe.Multiple attendances on the same day were only included once.

Outpatient attendances
Only outpatient appointments marked as having been attended were included.

Inpatient admissions
Inpatient admissions are recorded in HES as a series of 'Finished Consultant Episodes' (time spent under a particular consultant's care).Sometimes a patient's stay in hospital includes successive periods under the care of different consultants.We linked these episodes to form single admissions using the University of York Centre for Health Economics 'Continuous Inpatient Spell' definition.Because the person identifier for HES changed during the 2019-2020 financial year, we used the mapping files provided by NHS Digital to allow for continuous inpatient spells that started in financial year 2018-2019 but finished in 2019-2020 (the date across files where the person identifier changed).

Inpatient admissions with an ambulatory care sensitive condition
Admissions were flagged if they were related to an ambulatory care sensitive condition (ACSC) based on the classification used by Bardsley et al. 24 Emergency inpatient admissions Admissions were defined as emergency admissions based on the HES data classification.

Emergency readmissions
We used the University of York Centre for Health Economics definition for readmissions within 30 days of discharge, and included only emergency-coded admissions.

Length of stay
Days calculated for continuous inpatient spells, and included based on the date of admission.

Intervention
We used (primarily) trust statutory financial reporting, but combined with searches of primary care workforce data, Care Quality Commission (CQC) practice ownership datasets, and reviews of awarded contracts for delivering primary care services, to identify where vertical integration had taken place. 19e identified the date of vertical integration primarily from trusts' statutory financial reports, but also from practice websites and local and trade press.All vertically integrated practices are identified using a unique practice code, which is an organisation code that uniquely identifies each general practice in England.

Counterfactual
Vertical integration is one of several new organisational models affecting NHS primary care.Horizontal merger between general practices is a second; and use of Alternative Provision of Medical Services (APMS) contracts is a third.As a counterfactual, we used patients from a random sample of 'stable' practices; by which we mean practices that are neither vertically integrated, nor merged with other practices, nor changed contract type since April 2013 but remained on a General Medical Services (GMS) contract.As a supplementary analysis, we compared the impact of vertical integration for practices integrated with acute hospital trusts compared with those integrated with community trusts (we use the term 'community trust' as shorthand for any trust that does not run an acute hospital).This approach enabled us to match on the challenges that practices may experience before vertically integrating and explore the impact of integrating specifically with acute hospitals.Details of the methodological work underpinning this counterfactual approach overall are published separately. 19o identify practices that change contract type, we used annually reported data from NHS Digital. 21o identify horizontal mergers between practices we used person-level HES data from April 2013-February 2020, tracing the new practice codes of patients attending hospital outpatient services where earlier practice codes subsequently disappeared. 19,22

Analysis
We obtained data from NHS Digital covering the period from 1 April 2013-1 February 2020 because of the profound impact of the COVID-19 pandemic on secondary care utilisation after February 2020.To balance length of follow-up period against the number of vertically integrated practices in the resulting sample, we included practices for which follow-up of at least 2 years pre-integration and 2 years post-integration was possible.Thus, these are practices where vertical integration occurred between 1 April 2015 and 1 February 2018.Where vertically integrated practices had undergone horizontal mergers during the analysis period (1 April 2013-1 February 2020), we included the practice as a single merged practice in the analysis across the whole period.
In our first analysis, we described secondary care utilisation in the pre-intervention period before any practice underwent vertical integration (2014-2015) for all vertically integrated and control practices.
In our second analysis, we used a multivariable difference in difference framework adjusting for person-level age, sex, deprivation, calendar month, and year.We used a separate categorical flag for each month to account for both secular trends and seasonal variation, a flag for whether practices were intervention (vertical integration) or control practices, and a flag (in intervention practices) for whether the time period included was before or after the date of the intervention.We adjusted separately for time (as a linear variable) before and after the date of the integration in intervention practices to account and control for potential differences in pre-intervention trends in intervention practices compared with control practices.We additionally included the following: a random effect for practice; a random slope for the intervention to allow the impact of the intervention to vary between practices; and a random slope for year to allow trends over time to vary between practices.For intervention practices, we only included the 2 years before and after the intervention, but for control practices, we included all time periods to allow adjustment for secular trends.For all outcomes except length of stay, we used Poisson models, for length of stay we used a linear model.
In a further multivariable difference in difference analysis, only vertical integration practices are included and practices that integrated with an acute hospital trust are compared directly with practices that integrated with a community trust.

Results
Fifty-nine practices vertically integrated between 1 April 2015 and 1 February 2018, and horizontal mergers by February 2020 mean that these are included in the analysis as 42 distinct practices across the whole study period.Three of these practices have been excluded because of data-quality issues, particularly around organisation coding in HES identified in preliminary analyses.Thus, 39 vertically integrating practices are included in the analysis; 25 integrated with acute trusts and 14 with community trusts.Five hundred control practices were sampled, with 492 included after exclusions for poor data quality.
Table 2 shows the median rates at which patients of practices that went on to vertically integrate were using hospital services in financial year 2014-2015.There were 0.31 (median) A&E attendances per patient per year at vertically integrating practices, slightly higher than the 0.29 A&E attendances per patient in control practices.Vertically integrating practices also had slightly higher median rates of inpatient admissions and readmissions than control practices.The median rate of outpatient attendances was the same in vertically integrating and control practices.The mean hospital length of stay for patients at the median vertically integrating practice was slightly shorter, at 2.84 days, than at the median stable practice, 2.94 days.Median outpatient attendance rates were lower and emergency readmission rates higher in practices that integrated with community compared with acute trusts.
The impact of general practices vertically integrating with trusts on the rates at which their patients use hospital services are shown in Table 3.On average, in the 2 years after becoming vertically integrated, the rate of A&E attendances in the integrating practices fell by (a modest, but statistically significant) 2% (incidence rate ratio [IRR] 0.98 [95% confidence interval CI = 0.96 to 0.99], P<0.0001).Vertical integration is also associated with a 1% reduction in the rate of outpatient attendances  .00],P = 0.039) when it is first introduced.There was no evidence that vertical integration had any impact on length of inpatient stay.The falls in A&E and outpatient attendance rates appear to be temporary, as these grow at faster rates than control practices during the 2 years of follow-up after vertical integration.Comparing practices that vertically integrate with acute hospital trusts with practices that integrate with community trusts (see Table 4), the rate of A&E attendances shows a differential step-change fall at the date of vertical integration that is 3% more when integration is with an acute hospital trust than when it is with a community trust (IRR 0.97 [95% CI = 0.95 to 0.99], P = 0.01).But the rate of inpatient admissions is 4% more in vertical integration with acute trusts than with community trusts (IRR 1.04 [95% CI =1.01 to 1.06], P = 0.0095).There are no other statistically significant differences in step changes between vertical integration with an acute trust or a community trust.
Although we found no differential impact between the two types of trusts at the date of vertical integration with respect to outpatient attendances, we note that in practices that vertically integrate with acute hospitals, the post-integration rate of outpatient attendances does increase over the next 2 years at a considerably faster rate than in practices that integrate with community trusts (IRR 1.13 [95% CI = 1.03 to 1.24)] per year, P = 0.013).There are no statistically significant differences in postintegration trends in rates of other types of hospital use, comparing practices that integrate with acute trusts with practices that integrate with community trusts (Table 4).

Discussion Summary
Our work has provided evidence of the impact on hospital utilisation of vertical integration in the NHS in England between trusts (providers of secondary care) and general practices (providers of primary care).By comparing trends over time for vertically integrating general practices with those that did not merge with another practice or trust and did not change the form of contract they hold, we have found that vertical integration is associated with modest step-change reductions in patients' rates of the following: A&E attendances (-2%); outpatient attendances (-1%); emergency admissions (-3%); and emergency readmissions (-5%).We found no association with changes in rates of overall inpatient admissions or admissions for ambulatory care sensitive conditions; nor with length of stay.The falls in A&E and outpatient attendance rates are temporary; these rates resume growing at faster rates than for control practices, which offsets the initial step-change reduction within 1 or 2 years.There was little difference in the impact of vertical integration when comparing integration with acute hospital trusts and integration with community trusts.

Table 2
Pre-intervention (2014-2015)rates of use of hospital services by patients of vertical integration practices and a sample of stable practices ACSC = ambulatory care sensitive condition.A&E = accident and emergency.IQR = interquartile range.

Table 3
The impact on hospital use of vertical integration compared with control practices

Table 4
The impact on hospital use of vertical integration with acute hospital trusts compared with vertical integration with community trusts Percentage point step change for acute minus that for community vertical integration practices Additional yearly change after the intervention for acute compared with community vertical integration