Data Resource Profile: Hospital Episode Statistics Admitted Patient Care (HES APC)

Hospital Episode Statistics Admitted Patient Care (HES APC) data are collected on all admissions to National Health Service (NHS) hospitals in England. HES APC also covers admissions to independent sector providers (private or charitable hospitals) paid for by the NHS.1 It is estimated that 98–99% of hospital activity in England is funded by the NHS.2 A hospital admission includes any secondary care-based activity that requires a hospital bed, thus including both emergency and planned admissions, day cases, births and associated deliveries. HES APC does not cover accident and emergency (A&E, emergency department) attendances or outpatient bookings; these data are held in separate HES databases. All HES databases are collated and curated by NHS Digital (previously the Health and Social Care Information Centre). In the financial year 2014/15 (April to March), 18 731 987 hospital episodes from 451 different NHS hospital trusts (known as ‘providers’) were recorded in HES APC.3 The need for national data collection on hospital activity to inform management and planning of services was first recognized in the early 1980s by a Department of Health working group.4 Following these recommendations, a national programme was progressively rolled out, starting in 1987 and obtaining continual national coverage by (financial year) 1989/90.5 Since 2004/05, HES APC has also served as the basis for ‘Payment by Results’ (PbR), a pay-for-performance system of secondary care reimbursement in the NHS internal market.6 HES APC data files are structured according to financial years. Each row in HES APC indicates a ‘Finished Consultant Episode’ (FCE). An FCE represents a continuous period of care under one consultant, and each is specified with a start and an end date. Episodes are labelled as ‘finished’ and entered in HES APC according to the financial year in which they end. Consequently, episodes that start in one financial year and end in another will be classified as unfinished in the starting financial year, and finished in the ending financial year. Unfinished episodes need to be removed before analysis to prevent double counting. A hospital admission in HES APC is referred to as a ‘spell’, defined as an uninterrupted inpatient stay at one hospital. A spell may include several FCEs if the patient was seen by multiple consultants during the same stay, but does not include transfers between hospitals. If a patient is transferred to a different hospital, a new spell begins. In order to identify and measure continuous hospital stays, which include transfers to other hospitals, continuous inpatient spells (CIPs) need to be derived. Although CIP identifiers are not provided in standard HES APC extracts, methods for linking FCEs into CIPs are available,7 including that recommended by NHS Digital.8 HES APC has been frequently used for research and service evaluation, due to its universal coverage, long period of data collection and the ability to follow individuals over time. HES APC offers the opportunity to estimate population-based admission and procedure rates by condition and type of procedure, compare hospital performance and create hospital-based cohorts for short- or long-term follow-up. Since HES APC covers all births in NHS hospitals, representing 97.3% of births in England,9 it is also possible to create nationally representative birth cohorts. Upon discharge from the care of a particular consultant, the treating clinician completes a discharge summary for the patient of diagnoses made and procedures carried out during that FCE (where procedures include surgery, diagnostic imaging, ventilation and infusion/transfusion therapy). Discharge summaries are forwarded to a clinical coding department in the hospital, who enter the information onto the local electronic patient information database. Clinical coders undergo nationally accredited training programmes and follow standardized rules for translating information on discharge summaries into clinical codes.10,11 Every month, data are extracted from local hospital databases to the Secondary User Service (SUS), a national data warehouse housed within NHS Digital.12 Data from the SUS are extracted both for purposes of hospital reimbursement under PbR, and separately to create a provisional monthly HES extract. NHS Digital carry out basic data checks and cleaning, add geographical fields based on patient postcodes, and attach pseudonymized patient identifiers (‘HESIDs’) to each episode.13,14 At the end of each financial year, NHS Digital allow hospitals one further data submission to HES (the ‘Annual Refresh’), after which a provisional annual HES extract is produced for final review by hospitals. Once the Annual Refresh has been checked, a final annual HES dataset is made available.12 From 1997/98 onwards (when patients’ NHS numbers became a mandated return from hospitals), HES APC episodes have been linked longitudinally to the same patient by tagging episodes with the HESID. This alphanumeric variable allows patient follow-up, yet avoids the need for supplying patient identifiers to researchers. The methods used to generate the HESID have been described elsewhere.15 Each HES APC extract contains a unique set of HESIDs to reduce the risk of individual disclosure through merging separate data extracts supplied to different research teams. HES APC data can be linked to other datasets held by NHS Digital, including HES A&E attendances (from 2007/08), HES Outpatient appointments (from 2003/04), adult critical care (from 2008/09), diagnostic imaging data (covering all radiology procedures from 2012/13), the Mental Health Services Dataset (for all adult community and outpatient mental health care contacts from 2006/07) and Patient Reported Outcome Measures (pre- and postoperative questionnaires filled out by patients undergoing knee or hip replacements, varicose vein surgery or groin hernia repair from 2009/10). Secondary users can link these datasets because the same HESID algorithm is applied to each dataset. HES APC is also routinely linked to a number of external datasets. The Clinical Practice Research Datalink,16 a large UK primary care database, is linked to HES APC on a monthly basis. HES APC is linked to dates and causes of non-hospital deaths from the Register of Deaths in England and Wales held by the Office for National Statistics (for deaths registered since 1 January 1998), also on a monthly basis.17 Only deaths of patients recorded in HES APC are available through this linkage (i.e. deaths of persons who have not had a hospital admission since April 1997 are not included). NHS Digital also provides a trusted third-party bespoke linkage service, through which secondary users can request that HES APC data be linked to other external datasets. For example, both national disease registries (such as the National Joint Registry18 and the UK Renal Registry19) and well-established cohort studies including Whitehall II20 and the Hertfordshire Cohort Study21 have been linked to HES APC. Secondary users need to obtain the appropriate approvals to enable these linkages. HES APC provides detailed clinical, demographic and organizational information for each FCE (see Table 1), with 270 variables available in the core dataset. Apart from data on diagnoses and procedures, HES APC contains information on dates of admission, operations and discharge, admission method (e..g. emergency or planned), care provider and many geographical variables mapped from a patient’s postcode. The local health geographies and hospital providers in England have changed several times since 1997, and thus care needs to be taken to ensure continuity when carrying out local or provider level analyses that use HES APC data covering many years. Selection of key data fields available for each finished consultant episode (FCE) in HES APC data22 HESID Age at admission Age at discharge Sex Ethnic group Episode start date Episode end date Date of admission Date of discharge Admission method (e.g. - planned, emergency, birth) Discharge method Admission source Discharge destination Waiting time (from date of decision to admit to date of admission) Diagnoses (up to 20) Operations (up to 24) Operation dates (up to 24) Consultant specialty (admitting and treating consultant) Government office region Local authority Clinical commissioning group Index of multiple deprivation (IMD) 2004 rank, deciles and domains Care provider (hospital) General practice of patient Gestational age Number of previous births Birth weight Maternal age Mode of delivery Baby number (for multiple births) HESID Age at admission Age at discharge Sex Ethnic group Episode start date Episode end date Date of admission Date of discharge Admission method (e.g. - planned, emergency, birth) Discharge method Admission source Discharge destination Waiting time (from date of decision to admit to date of admission) Diagnoses (up to 20) Operations (up to 24) Operation dates (up to 24) Consultant specialty (admitting and treating consultant) Government office region Local authority Clinical commissioning group Index of multiple deprivation (IMD) 2004 rank, deciles and domains Care provider (hospital) General practice of patient Gestational age Number of previous births Birth weight Maternal age Mode of delivery Baby number (for multiple births) Selection of key data fields available for each finished consultant episode (FCE) in HES APC data22 HESID Age at admission Age at discharge Sex Ethnic group Episode start date Episode end date Date of admission Date of discharge Admission method (e.g. - planned, emergency, birth) Discharge method Admission source Discharge destination Waiting time (from date of decision to admit to date of admission) Diagnoses (up to 20) Operations (up to 24) Operation dates (up to 24) Consultant specialty (admitting and treating consultant) Government office region Local authority Clinical commissioning group Index of multiple deprivation (IMD) 2004 rank, deciles and domains Care provider (hospital) General practice of patient Gestational age Number of previous births Birth weight Maternal age Mode of delivery Baby number (for multiple births) HESID Age at admission Age at discharge Sex Ethnic group Episode start date Episode end date Date of admission Date of discharge Admission method (e.g. - planned, emergency, birth) Discharge method Admission source Discharge destination Waiting time (from date of decision to admit to date of admission) Diagnoses (up to 20) Operations (up to 24) Operation dates (up to 24) Consultant specialty (admitting and treating consultant) Government office region Local authority Clinical commissioning group Index of multiple deprivation (IMD) 2004 rank, deciles and domains Care provider (hospital) General practice of patient Gestational age Number of previous births Birth weight Maternal age Mode of delivery Baby number (for multiple births) Socioeconomic status is measured by the Index of Multiple Deprivation 2004 (IMD), a small area-based indicator constructed from several different measures of deprivation.22 IMD is measured at Lower Super Output Area (LSOA) level, where an LSOA contains between 400 and 1200 households.23 Individual-level measures of socioeconomic status (e.g. education level or income) are not available. Detailed information on variables available, specific cleaning rules and coding used are available in the HES APC Data Dictionary provided by NHS Digital.24 Diagnoses are coded using the International Classification of Diseases version 10 (ICD-10).25 ICD-9 was used between April 1989 and March 1995. The number of diagnosis fields has increased over time: since April 2007, each FCE can have up to 20 ICD-10 codes entered (up from 7 codes before April 2002 and 14 in April 2002–March 2007). Each FCE has one primary diagnosis, which accounts for the majority of the length of stay of the FCE. The other diagnoses are referred to as comorbidities. According to NHS Digital cleaning rules, each FCE must have at least one primary diagnosis, although it may be recorded as unknown (ICD-10 code R69). Operations and other interventions are coded using a UK-specific system, the Office of Population Censuses and Surveys Classification of Interventions and Procedures (OPCS, currently version 4.7).26 This has evolved over time as new techniques and technologies have been introduced. A history of versions in use is available from the NHS Digital coding standards website.26 Each FCE may have up to 24 operations recorded (up from 4 before April 2002 and 12 in April 2002–March 2007), but procedure fields are left empty if patient management did not require an intervention covered by OPCS (e.g. where the primary treatment was a drug regimen or observation). A primary procedure is selected for each FCE as that which is the most resource-intensive, but a procedure may be described using more than one code to indicate surgical approach, anatomical location and side of procedure (e.g. stent placed under radiological control in femoral artery of left leg). Dates are also entered for each procedure. Each birth event in HES APC generates at least two FCEs: one delivery episode and one or more birth episodes. Each delivery and birth episode includes an additional ‘maternity tail’, with detailed fields including the baby’s birthweight, gestational age, birth order (for multiple births), mode of delivery and maternal age (Table 1). The maternity tail is based on information entered via local maternity databases. Unlike the diagnostic and procedure fields, the maternity tail data fields use HES-specific categories rather than standardized classifications, and it is not a mandated return to NHS Digital. This leads to large variations in data completeness and quality.27,28 It is not possible to directly link a mother and a baby in HES APC; that is, the mother’s HESID is not copied to the baby’s birth record. However, linkage between mother and baby is possible using probabilistic methods.29 Both numbers and rates of hospital admissions have increased during the period of HES APC data collection (Figure 1), particularly among older adults (aged 60-74 and 75+). Between 1998/99 and 2014/15, the overall FCE rate has increased by 40% from 24.5 per 100 person-years to 34.3 per 100 person-years, with the steepest increase (73.0%) in adults aged 75+. A) Number of finished consultant episodes (FCEs) by age group from financial years 1998/99 to 2014/15; and B) episode rates by age group per 100 person-years. Denominators for rates are based on mid-year population estimates for England78. Since HES APC covers all hospital admissions, infants and older adults (aged 65+) are over-represented in HES APC compared with the general population of England (Table 2). Demographic characteristics of HES APC patients compared with general population of England Numbers within parentheses represent proportions of FCEs (for HES APC) and proportions of persons (for England) aData source: HES APC 2014–15.3 bONS 2014 mid-year population estimates.75 Demographic characteristics of HES APC patients compared with general population of England Numbers within parentheses represent proportions of FCEs (for HES APC) and proportions of persons (for England) aData source: HES APC 2014–15.3 bONS 2014 mid-year population estimates.75 Although no up-to-date bibliography of published research based on HES APC is curated by the data providers, a 2013 systematic review identified 148 articles using HES APC data published between 1989 and July 2011.30 We carried out a subsequent search on PubMed on the 8 June 2016 using the search term ‘Hospital Episode Statistics’ for article abstracts published since July 2011. We identified 264 relevant publications where the primary analysis involved the use of HES APC data, and a further 130 papers where HES data had been linked to cohorts created in other datasets. The annual number of publications using HES APC data has increased from 2 in 199330 to 88 in 2015. Published studies using HES APC data have covered a diverse range of topics. They have explored the incidence of conditions across regions and over time.31,32 They have also examined cross-sectional and longitudinal patterns of treatment by organization,33 including comparing NHS and privately contracted providers34 or regions,35,36 both from descriptive and analytical perspectives. Regional comparisons have included evaluating the impact of clinical evidence37 or guidelines38 as well as health care policies.39 They have examined the outcome of medical as well as surgical therapies (such as survival,40 short-term postoperative mortality,41 complications,42 reoperation43 and hospital readmissions44), with some seeking to identify factors that are associated with these outcomes, in terms of both patient characteristics45,46 and organizational factors such as surgical volume47 or day of week.48 studies include coding risk and using methods to data routinely produced on the of secondary care are based on HES APC include hospital produced by NHS and and research by independent and The key of the HES APC is its universal coverage, which provides an of hospital episodes. The large of HES APC it possible to estimate admission rates and for including or specific is the to longitudinally link patients using the for the of cohort studies if a date can be The long period of data collection of HES up to allows long-term of which has the of risk for ICD-10 coding of clinical diagnoses offers the opportunity to use HES APC for comparisons of secondary care Since ICD-10 is used in hospital data across the and HES APC has been used to the impact of health between NHS and International studies using HES APC include comparisons of the incidence of and comparisons are due to between in admission of care and secondary care is at of use or requires health or other HES APC episodes are linked to information on of due to the ability to each episode to a and a This HES APC an data for health of the key in HES APC is the on diagnostic and procedure codes for and coding rules, clinical coders on the and of discharge summaries to enter data Consequently, diagnostic coding between hospitals, particularly for Since the of PbR, financial for hospitals to coding in order to ensure This has to an increase in the number of diagnostic codes used and in coding The of for studies using HES APC data, and care must be taken to not of Since HES APC covers it is to between hospitals or over time in admission The of the in A&E in 2004 has been as a for the increase in rates of emergency admissions in during the in for emergency admissions can be examined using linked HES A&E in admission for planned procedures be using HES datasets. Although age, and clinical characteristics are well in HES APC (see Table data on are has been a mandated return for all NHS contacts since Although has over the of patients with a recorded was in up from in is a of data in the maternity tail fields (see 2). were not extracted from the SUS for birth episodes to which birth episodes be mapped to geographical including the Index of Multiple Deprivation an example, completeness of the IMD variable for birth episodes in was compared with in of birth with data for selected variables in the maternity tail from financial years 1997/98 to The HESID linkage algorithm on the of NHS number across all hospital episodes to that have to link to a Consequently, is a of in HES APC. A estimate the HESID rate at to an of rates by NHS numbers were not provided at birth that linkage within HES APC and to other HES and external datasets is not for births before HES APC covers or care but it does not to identify such stays, detailed information on level of care or A separate HES dataset covers adult critical care from data to or care are collected through external to NHS Digital. Data on through hospital to are not available in HES APC. is currently no national hospital for England. who not to NHS Digital can a 2 with primary care From April any in previous financial to persons who have out in any NHS Digital dataset HES APC) will be removed before to secondary for the 2014/15 HES APC annual of episodes will be with geographical in to HES APC data is provided by NHS Digital for the and health care an extract of the data must that will health and care and Data be for Data are through the Data Service are by the Data which all data for data to is an appropriate basis for data and that appropriate data is in HES and associated are available on the NHS Digital out to that data users the terms and conditions of including disclosure HES APC contains data on all admissions to National Health Service (NHS) hospitals in or to independent hospitals where the are by the It was set up for purposes of management and planning of hospital Data are also collected for purposes of hospital HES APC includes all hospital care episodes from the financial year onwards April March patient identifiers that allow for longitudinal of patients are available from 1997/98 HES APC data are entered from medical by clinical coders in each hospital, according to national clinical coding The is collated and by NHS Digital (previously the Health and Social Care Information Centre). Data fields for procedures, patient and admission and discharge hospital and other HES APC data can be linked to outpatient and emergency department attendances as well as datasets external to NHS Digital, including data are via the NHS Digital and data are available through the NHS Digital Data to and a is by from the Department of Health Research through to the Research in the Health of and number This is an independent and funded by the Department of The are not of the is by to the of Health from the Research Research Research and Social Research and Research National for Health National for Social Care and Health Research and is funded by a National for Health Research This article represents independent research funded by the National for Health Research The are of the and not of the the or the Department of of We are to for this