Assumptions used in estimating a population benchmark

The assumptions used in estimating a population benchmark rate for referral into a urinary continence service of 0.80% per year are based on the following sources of information:

• epidemiological data on the prevalence/incidence of urinary incontinence (UI) and overactive bladder syndrome (OAB) in the adult female population
• activity data to establish the rate of surgery for UI in women
• current practice to establish the number of women with UI and OAB in contact with GP services
• published research on UI and OAB
• expert clinical opinion of the topic-specific advisory group, based on experience in clinical practice and literature review.

The adult female population has been defined as women aged 15 years and older. This is due to the availability of activity data and population data at general practice level within certain age bands and its use within the commissioning and benchmarking tool.

Epidemiological data

Differences in study populations, definitions and measurements, and the survey methods used result in a wide range of prevalence estimates for UI in the female population. Where the most inclusive definitions have been used (‘ever', ‘any', ‘at least once in the last 12 months') estimates in the adult female population range from 5% to 69%, with most studies reporting prevalence in the range 25-45%^[1].

Stress UI is estimated to be the most prevalent type of UI, accounting for around 41% of cases; urge UI accounts for around 16% and mixed UI for around 34% of the total^[2].

OAB is defined as urgency that occurs with or without urge UI and usually with frequency and nocturia. The estimated prevalence of OAB in the UK is around 10% of the adult female population^[3]. Around 33% of people with OAB are also believed to have UI^[4,^5]. The prevalence of UI and OAB increases with age, and some populations - such as those with a higher number of nursing homes - may have a greater prevalence of UI than the population as a whole^[6]. However, most people with UI and OAB do not report symptoms to their GP^[7].

Activity data - ‘Hospital episode statistics' data

The ‘Hospital episode statistics (HES)' 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.

In 2005/06 the rate of surgery for female UI was 40 per 100,000 of the adult female population with large variation across the country. The insertion of tension-free vaginal tape (TVT) slings was the most common procedure, accounting for 80% of all procedures for UI.

Surgery is recommended only after failed conservative management of UI. A recent audit of the adherence to the NICE technology appraisal on the use of TVT slings (replaced in 2006 by the NICE clinical guideline CG40 on urinary incontinence) for stress UI, found that conservative measures had not been attempted in around 50% of women undergoing the procedure. This may mean that some of these procedures could have been avoided[8].

If the result of this audit was reproduced across the country, capacity within continence services providing conservative management would need to increase, but the number of surgical procedures performed for UI could be expected to decrease.

Current practice

Data from IMS Disease Analyser, a database that holds patient data from a sample of GP practice systems, suggests that around 4% of the female population aged 15 years and older have diagnosed UI; the annual incidence of diagnosed UI (that is, the annual detection rate of new cases) is 0.43% of the adult female population. These estimates include a minority of women who have both faecal incontinence and UI (double incontinence).

Research from the General Practice Research Database (GPRD) suggests that the prevalence of diagnosed OAB is 0.34% of the adult female population and the annual incidence of diagnosed OAB is 0.24% of the adult female population.

Taking into account an estimated 33% overlap between UI and OAB^[4,^5] the prevalence of diagnosed UI/OAB is estimated to be around 4.22% of the adult female population aged 15 years and older, and the annual incidence of diagnosed UI/OAB around 0.59% of the adult female population.

The quality of data used in the analysis of diagnosed UI and OAB relies on the information recorded within patients' medical records. In particular, poor recording of UI and OAB symptoms may have led to an underestimation of the total numbers of women in general practice with diagnosed UI/OAB.

Published research

Research based on a large sample of women attending GP services for any reason found that the prevalence of UI was 54% of the adult female population, of whom around 47% reported symptoms to their GP. If this study was a reflection of GP services across the country, estimates of UI based on current practice (see above) represent only half of the population of women with UI that are currently in contact with services^[7].

Research from the Leicestershire MRC Incontinence Study (2000) of people over 40 years of age suggested that, at any one time in the population, around 1.28% of the adult female population had significant urinary symptoms and had a preference for some form of treatment.

Expert clinical opinion

The consensus opinion of the topic-specific advisory group was that the women with UI identified in GP services are those seeking help for their UI/OAB, and therefore the take up of services would be high, at around 80-90%.

Conclusions

Based on the epidemiological data and other information outlined above, it is concluded that the benchmark for referral into a urinary continence service is 0.80% of the adult female population per year. This is based on the following assumptions:

• in current practice the average detection of new cases of UI and OAB per year is 0.59% of the adult female population
• around 1.28% of the adult female population at any one time have significant urinary symptoms and a preference for some form of treatment
• the mid point figure of those noted above is 0.94%
• take up of a urinary continence service would be around 85% (based on the mid point of estimates advised by the topic-specific advisory group).

Therefore the population benchmark for a urinary continence service is estimated to be 0.80% of the adult female population per year.

Use the urinary continence service commissioning and becnhmarking 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 Collaborating Centre for Women's and Children's Health (2006) Urinary incontinence. Full national clinical guideline on the management of urinary incontinence in women. London: RCOG Press.
2. Hunskaar S, Lose G, Sykes D et al. (2004) The prevalence of urinary incontinence in women in four European countries. British Journal of Urology International 93: 324-30.
3. Irwin I, Milsom K, Reilly K et al. (2006) Prevalence of overactive bladder syndrome: European results from the epic study. European Urology 5 (Suppl.): 115.
4. Tubaro A (2004) Defining overactive bladder: epidemiology and burden of disease. Urology 64 (Suppl. 1): 2-6.
5. Reilly K, Milsom I, Irwin D et al. (2006) Prevalence of incontinence and overactive bladder: European results from the epic study. European Urology 5 (Suppl.): 116.
6. Durrant J, Snape J (2003) Urinary incontinence in nursing homes for older people. Age and Ageing 32:12-8.
7. Shaw C, Das Gupta RD, Bushnell DM (2006) The extent and severity of urinary incontinence amongst women in UK GP waiting rooms. Family Practice 25: 497-506.
8. Ismail SIMF (2007) Audit of compliance with NICE guidelines on the use of tension-free vaginal tape slings for stress incontinence. Journal of Obstetrics and Gynaecology 27: 469-99.