Assumptions used in estimating a population benchmark

The assumptions used in estimating a population benchmark rate for direct admission to an acute stroke unit (120 per 100,000 population - 100% of people admitted to secondary care following a stroke) and treatment of ischaemic stroke with alteplase (11 per 100,000 population - 9% of people admitted to secondary care following a stroke) are based on the following sources of information:

• epidemiological data on the incidence of stroke
• hospital episode statistics to establish number of admissions for stroke
• expert clinical opinion of the topic-specific advisory group, based on experience in clinical practice and literature review.

Epidemiological data

Estimates of the population-wide incidence of stroke vary widely depending on the definitions used and the types of populations studied.

The 2005 National Audit Office report Reducing brain damage: faster access to better stroke care suggested that the population-wide incidence of stroke is 0.22% per year. This includes both first and recurrent strokes, and equates to around 110,000 people per year. The incidence of stroke is likely to vary around the country based on the demographic characteristics of the population and the prevalence of vascular risk factors such as diabetes and hypertension^[1]. The same report suggests that around 85% of strokes are ischaemic strokes.

Activity data - ‘Hospital episode statistics' data

The ‘Hospital episode statistics' database contains details of all admissions to NHS hospitals in England. It includes private patients treated in NHS hospitals, patients who were resident outside England and care delivered by treatment centres (including those in the independent sector) funded by the NHS.

Data were extracted to determine the number of people who were admitted to secondary care as an emergency following a stroke. The International classification of diseases (ICD) (10th revision) codes used to define stroke were:

• 161: intracerebral haemorrhage
• 163: cerebral infarction
• 164: stroke not specified as intracerebral haemorrhage or cerebral infarction.

Analysis suggests that around 63,000 people were admitted as an emergency following a stroke in 2006/07- approximately 0.12% of the population (120 per 100,000).

This estimate (63,000) is lower than the population-wide estimate (110,000) because it does not include a significant proportion of strokes that result in death or that occur in hospital. There may also be coding issues, for example, where a stroke has been coded with an ICD10 code other than those listed above.

The NICE clinical guideline CG68 on stroke recommends that all people with suspected stroke should be admitted directly to a specialist acute stroke unit following initial assessment. However, the National sentinel stroke audit - organisation of care (phase I) states that this model is only used in 16% of hospitals with 81% of people going to a generic admission unit following a stroke.

A proportion of people admitted following a stroke will be suitable for treatment with alteplase, as outlined in the NICE technology appraisal TA122 Alteplase for the treatment of acute ischaemic stroke. The proportion of people who receive alteplase will depend on the timing of admission following a stroke, how soon brain imaging or scanning can be performed to rule out haemorrhagic stroke, and the number who are younger than 80.

In 2006/07 around 50% of people admitted to secondary care following a stroke were younger than 80. This equates to around 60 per 100,000 population. Around 85% of these people are likely to have had an ischaemic stroke (see Epidemiological data above).

Expert clinical opinion

The consensus opinion of the topic-specific advisory group was that around 20% of people who have had an ischaemic stroke and are younger than 80 should be eligible to receive alteplase. However, this should not be seen as a limit, as the proportion of people who are eligible to receive alteplase could increase with more timely access to diagnostic scans.

Conclusions

Based on the epidemiological data and other information outlined above, it is concluded that on average around 120 per 100,000 population (100% of people admitted to secondary care following a stroke) will require admission to an acute stroke unit, and around 11 per 100,000 population are expected to require treatment with alteplase for ischaemic stroke. This is based on the following assumptions:

• The rate of admission to secondary care following a stroke, based on 2006/07 data, was 120 per 100,000 population, of which 100% should be admitted directly to an acute stroke unit.
• Of the 60 per 100,000 population who are younger than 80 and admitted following a stroke, 85% are likely to have had an ischaemic stroke and 20% of these (based on the consensus opinion of the topic-specific advisory group) would be eligible to receive treatment with alteplase. This equates to 11 per 100,000 population, or approximately 9% of people admitted following a stroke.

Therefore the population benchmark for admission to an acute stroke unit is 100% of people admitted to secondary care following a stroke or 120 per 100,000 population based on the national average, per year.

The population benchmark for receiving treatment for ischaemic stroke with alteplase is 9% of people admitted to secondary care following a stroke or 11 per 100,000 population based on the national average, per year.

Use the acute stroke service commissioning and benchmarking tool to determine the level of service that might be needed locally and to calculate the cost of commissioning the service using the indicative benchmark and/or your own local data.

References

1. National clinical guideline for diagnosis and initial management of acute stroke and transient ischaemic attack (TIA) (2008). London: Royal College of Physicians.

2. Clinical Effectiveness and Evaluation Unit (2008) National sentinel stroke audit - organisation of care (phase I). London: Intercollegiate Stroke Working Party, Royal College of Physicians.