Assumptions used in estimating a population benchmark

The assumptions used in estimating a benchmark rate of 1.40% of the population requiring anticoagulation therapy per year are based on the following source of information:

• epidemiological data estimating the prevalence of conditions requiring anticoagulation therapy, namely atrial fibrillation (AF), deep vein thrombosis and patients with prosthetic heart valves.

Epidemiological data

Prevalence of atrial fibrillation

DeWilde^[1] and coworkers examined trends in the prevalence of diagnosed AF between 1993 and 2003 using data from 131 general practices (about one million registered patients annually) in the UK. They estimated, in 2003, the prevalence of active- and ever-diagnosed AF to be 1.31% and 1.49% respectively in men, and 1.15% and 1.29% respectively in women. The same research found that prevalence rose steadily with increasing age, with the prevalence of active AF in those aged 85 years and over to be 13.2% in men and 11% in women.

The proportion of people with AF who receive anticoagulation therapy (the uptake rate) currently varies in practice. DeWilde and coworkers found that 53% of males and 40% of females with AF were receiving oral anticoagulants, but in common with other research found that many who were eligible for anticoagulation therapy did not receive it. Published research^[2-6], suggests that the proportion of people with AF who are eligible for, but do not receive, anticoagulation could be between 20% and 40%.

The numbers of people diagnosed with AF and the proportion receiving anticoagulant or antiplatelet therapy is recorded in primary care as part of the revised Quality and Outcomes Framework (QOF). 2007/2008 QOF data indicates the national prevalence of diagnosed AF is 1.30%.

Using these data to estimate the proportion of people with AF who could potentially be receiving anticoagulation therapy, the following assumptions have been made:

• the average population prevalence of AF is 1.30% - derived from QOF data.
• the average proportion of patients with AF currently receiving anticoagulation therapy is 47%
• the additional proportion of patients with AF who could be receiving anticoagulation therapy is 30% (mid point of 20% and 40%).

Therefore, the proportion of the population requiring anticoagulation therapy would be 1% based on a population prevalence of AF of 1.30%, and a maximum uptake of anticoagulation therapy of 77%.

Prevalence of other conditions requiring anticoagulation therapy

Other major groups requiring anticoagulation therapy include patients with:

• deep vein thrombosis
• prosthetic heart valves.

There are no national data on the incidence of deep vein thrombosis (DVT). Anecdotal evidence^[7],[8] suggests that the incidence could be up to 0.17%. While anticoagulation therapy following DVT is not required in the long term, patients requiring treatment at any one time has been estimated at 0.2%. The use of anticoagulants for 3-6 months is sufficient for many patients^[9].

Data from the UK heart valve registry (UKHVR) indicate that approximately 0.2% of the population has prosthetic heart valves. All patients who receive a mechanical valve replacement are given lifelong anticoagulation. A proportion of patients with bioprosthetic valve replacement also receive anticoagulation for a variable period of time^[10].

Conclusions

Based on the epidemiological data above, the proportion of the population requiring anticoagulation therapy is estimated to be 1.4%. This comprises 1% with AF, 0.2% with DVT, and 0.2% with prosthetic heart valves.

Therefore a benchmark rate of 1.40% of the population requiring anticoagulation therapy is considered appropriate.

Use the anticoagulation therapy 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. DeWilde S, Carey IM, Emmas C et al. (2006) Trends in the prevalence of diagnosed atrial fibrillation, its treatment with anticoagulation and predictors of such treatment in UK primary care. Heart 92: 1064-1070.
2. Ruigomez A, Johansson S, Wallander MA et al. (2002) Incidence of chronic atrial fibrillation in general practice and its treatment pattern. Journal of Clinical Epidemiology 55: 358-363.
3. Batty GM, Grant RL, Aggarwal R et al. (2003) Using prescribing indicators to measure the quality of prescribing to elderly medical in-patients. Age and Ageing 32: 292-298.
4. White S, Feely J, O'Neill D (2004) Community-based study of atrial fibrillation and stroke prevention. rish Medical Journal 97: 10-12.
5. Mehta PA, Grocott-Mason R, Dubrey SW (2004) Adherence to anticoagulation guidelines for atrial fibrillation: a district general hospital survey. British Journal of Cardiology 11: 474-477.
6. Murdoch DL, O'Neill K, Jackson J et al. (2005) Are atrial fibrillation guidelines altering management? A community based study. Scottish Medical Journal 50: 166-169.
7. Nordstrom M, Lindblad B, Bergqvist D et al. (1992) A prospective study of the incidence of deep-vein thrombosis within a defined urban population. Journal of Internal Medicine 232(2): 155-160.
8. Hansson PO, Welin L, Tibblin G et al. (1997) Deep vein thrombosis and pulmonary embolism in the general population. ´The Study of Men Born in 1913'. Archives of Internal Medicine 157(15): 1665-1670
9. Kyrle PA, Eichinger S (2005) Deep vein thrombosis. Lancet 365: 1163-1174.
10. Vaughan P. Waterworth PD (2005). An audit of anticoagulation practice among UK cardiothoracic consultant surgeons following valve replacement/ repair. Journal of Heart Valve Disease14: 576-82