Geographically based systems

Numbers of emergency admissions for the set of 14 conditions for each emergency and urgent care system were calculated using Hospital Episode Statistics (HES) for the 3 financial years April 2008 to March 2011. Admissions from all sources were included. The most common admission route was EDs, with an average of 69% of avoidable admissions through this route, although this varied by system between 44% and 92%.

The condition code for the first finished consultant episode was used. PCT mid-2009 resident populations were then used as the denominator to calculate the rate of potentially avoidable emergency admissions per 100,000 population. The directly age- and sex-standardised admission rates per 100,000 per year were calculated for each PCT for the 3-year period using seven age groups (0–4, 5–14, 15–44, 45–64, 65–74, 75–84, 85+ years), standardised to the whole population for England in 2009. A 3-year period was selected to ensure that the effect of annual variability in emergency admission rates at a system level was minimised. It is important to understand that this rate is an indicator of avoidable admissions. It is based on conditions rich in avoidability; that is, not all admissions from these conditions were avoidable in practice. For shorthand, we call this the SAAR even though it was a directly standardised rate.

Acute trust-based systems

Catchment populations for acute trusts were needed to calculate admission rates for the 14 conditions. There are different ways of calculating catchment populations for hospitals, with debates about which approach is best.^31,32 We used estimates of acute trust catchment populations for emergency admissions in 2009 calculated by Public Health Observatories in England.³³ These catchment areas were defined as the number of people in each sex and age group who live in the catchment of the acute trust. They were calculated using HES data between April 2006 and March 2009 to count the number of patients in each age and sex group admitted from small areas called Middle Super Output Areas. These areas have a minimum population of 5000, with an overall mean of 7200. Mid-year population estimates for 2009 were supplied by the Office for National Statistics (ONS). Within each 5-year age and sex group, the proportion of patients who went to each acute trust as a proportion of patients who used any acute trust was calculated. For each small area, this proportion was multiplied by the resident population in that age and sex group to give the small area catchment population for each acute trust. Then the small area catchment populations for each acute trust were summed to give the total catchment population for each acute trust.

We calculated the SAARs per 100,000 per year for each acute trust for the 3-year period April 2008 to March 2011 using seven age groups (0–4, 5–14, 15–44, 45–64, 65–74, 75–84, 85+ years) standardised to the whole population for England in 2009. A 3-year period was selected to ensure that the effect of annual variability in emergency admission rates was minimised.

Some specialist acute trusts offer care to specific age, sex or condition groups only. We wanted to compare similar types of acute trusts and focused on general acute trusts because they account for the majority of emergency admissions.¹ We included any acute trusts where the estimated population in each age and sex group was > 1000. This was an arbitrary cut-off point which successfully excluded children’s hospitals, women’s hospitals and condition-specific hospitals. It also excluded some general acute trusts located near children’s hospitals because they did not admit children.

Geographically based systems

There were 152 geographically based systems (based on PCT populations). The reliability of the HES data was checked by looking for consistency between numbers of emergency admissions per year within each system. The only large differences between years for any system were two systems with zero emergency admissions for 2010–11. We excluded them from the analysis, leaving 150 systems.

The median SAAR was 2258 [interquartile range (IQR) 1808–2662], with a 3.4-fold variation between systems ranging from 1268 to 4359, and a 1.9-fold variation between the 10th and 90th percentiles. Geographical variation in the SAAR was apparent, with highest rates clustering in the north-west of England, the north-east of England and east London (Figure 2).

FIGURE 2

Variation in SAAR in 150 geographically based systems in England.

Acute trust-based systems

There were 131 acute trusts after exclusion of specialist hospitals. Two acute trusts had missing data for admissions in 2010/11 and were removed, leaving 129 acute trusts. The median SAAR was 1939 (IQR 1676–2331) per 100,000 population per year, with threefold variation between acute trusts ranging from 1194 to 3601, and a 1.8-fold variation between the 10th and 90th percentiles (Figure 3).

FIGURE 3

Variation in SAAR in 129 acute trust-based systems in England.

Standardised avoidable admissions rate and all emergency admissions

There was a strong association between the SAAR (2008–11) and the directly standardised rate for all emergency admissions for geographically based systems (2009–10) (Figure 4). Systems with high SAARs tended to have high rates of emergency admissions (Pearson’s r = 0.88, p < 0.001).

FIGURE 4

Relationship between SAAR and directly standardised rate of all emergency admissions rate by geographically based systems. DSR, directly standardised rate.

It is also worth noting that five of the conditions in our SAAR appeared in the top 10 diagnostic groups contributing to an increase in emergency admissions over recent years.¹

Standardised avoidable admissions rate and ambulatory emergency admissions

Ambulatory or primary care sensitive conditions are conditions for which hospital admission could be prevented by interventions in primary care. There are various definitions³⁴ but the King’s Fund list is the most frequently used in England.²² There is some overlap between these 19 ACSCs and our 14 conditions (indicated by * below):

• influenza and pneumonia
• other vaccine-preventable conditions
• asthma
• congestive heart failure
• diabetes complications*
• COPD*
• angina*
• iron-deficiency anaemia
• hypertension
• nutritional deficiencies
• dehydration and gastroenteritis
• pyelonephritis
• perforated/bleeding ulcer
• cellulitis*
• pelvic inflammatory disease
• ear, nose and throat infections
• dental conditions
• convulsions and epilepsy*
• gangrene.

Our SAAR is based on injuries as well as illness and includes mental as well as physical health problems. We could not locate ACSC rates for our systems but we did locate the rate of admissions with emergency ambulatory care conditions (EACCs) per population by PCT.³⁵ This is a directly age-, sex- and deprivation-standardised admission rate based on 49 emergency conditions with the potential to be managed on an ambulatory basis. The 49 conditions were developed by the National Institute for Improvement and Innovation. Figure 5 shows that there is correlation between our SAAR and the EACC (Pearson’s r = 0.34, p < 0.001) but that it is weaker than that between our SAAR and all emergency admissions.

FIGURE 5

Relationship between SAAR and admissions with EACCs by geographically based systems.