Scholze et al. BMC Public Health 2010, 10:529 http://www.biomedcentral.com/1471-2458/10/529 metabolism disturbances have also been found to cluster together. Such groupings of risk factors for cardiovascu- lar disease in the same hypertensive individual occur together more often than would be expected by chance alone, giving rise to a clinical entity that has been termed metabolic syndrome (MetS) [4]. The syndrome has been shown to significantly increase the risk of car- diovascular disease, type 2 diabetes and mortality [5-8]. In patients with hypertension it doubles the relative risk of cardiovascular disease [9-11] and triples the relative risk of type 2 diabetes [12]. Moreover, the risk increases with the number of MetS components present [10,13]. As there are 16 different conceivable combinations of risk factors that could be diagnosed as MetS not all can be weighted equally in terms of their impact on risk and for some combinations this increase in risk is controver- sial. However, what is known for sure is that the coexis- tence of hypertension disproportionately increases the risk of cardiovascular disease [14]. However, there is much debate as to whether MetS should be treated as a clinical entity in general practice or whether physicians should concentrate on treating individual risk factors. The primary purpose for diagnos- ing MetS in general practice is to identify patients who are at high long-term risk of developing cardiovascular disease and type 2 diabetes and who require lifestyle and/or pharmacological therapies to reduce this risk. Recent European guidelines on the management of patients with arterial hypertension consider those with hypertension and MetS as a special condition suggesting a different therapeutic approach compared to patients with hypertension alone [15]. Such recommendations are based on a number of evidence-based observations. In a position statement the European Society of Hyper- tension pointed out that in patients with hypertension and MetS the overall cardiovascular risk may be greater than the sum of its identifiable components and that MetS components are often defined by values lower than those defined in various individual risk factor guidelines which may lead to many patients with high cardiovascular risk not being identified [16]. They also point out that MetS risk factors are relatively easily identified in clinical practice. The clinical utility of diagnosing MetS in general prac- tice has been hampered by the inconsistency of the diagnostic criteria available. Some definitions appear to be better than others at identifying high risk patients in Europe. In studies using both the International Diabetes Federation criteria and those developed by the United States Adult Treatment Panel III of the National Cho- lesterol Education Program (ATP III) a much higher prevalence of MetS was identified by the International Diabetes Federation criteria [17,18] but these criteria led to much lower predictive power for coronary events Page 2 of 12 than the ATP III criteria [19]. This suggests that cur- rently the ATP III criteria are the most appropriate for European populations given that excessive over-diagnos- ing of the syndrome would subject the health service to unnecessary budget pressures. Relatively little is known about the epidemiological burden of MetS in patients with hypertension in the general population in Europe. Using ATP III criteria, European population studies suggest that the prevalence is around 8% to 13% [20-22]. The reported proportion of hypertensive patients that have MetS is wide-ranging. Population-based studies suggest the proportion is around 20% to 40% [20-23]. Primary care studies report that a fifth and up to just over a half of hypertension patients can be diagnosed with MetS [13,17,24-27]. No studies have assessed the economic burden of MetS in patients with hypertension. In order to fill this gap this study aims to model the health care costs of hypertension in three European countries (Germany, Spain and Italy) in 2008 and 2020 and to assess how the consequences of MetS in terms of associated type 2 dia- betes and the increase in cardiovascular events impacts on this economic burden. Methods Overview This study uses a prevalence-based approach that com- bined the demographics of the population with hyper- tension and MetS prevalence rates, incidence of cardiovascular disease, prevalence of type 2 diabetes and healthcare costs into a cost of hypertension and MetS model. A comprehensive literature review was con- ducted to identify inputs and data sources included national surveys, IMS Health Pharmaceuticals Sales data and published information. The model and the assump- tions used have been described in detail elsewhere [28]. Briefly we developed a prevalence-based model from the perspective of the health service (Figure 1). MetS was defined according to modified ATP III criteria, where an individual is defined as having MetS if they have three out of five diagnostic criteria: Abdominal obesity (waist; males > 102 cm, females > 88 cm), hyper- tension (≥140/90 mm Hg), low high-density lipoprotein (HDL) cholesterol (males <40 mg/dL, females <50 mg/ dL), high triglycerides (≥ 150 mg/dL) and impaired fast- ing glucose (≥ 110 mg/dL or known diabetes) [29]. We modified the criteria in relation to blood pressure from ≥135/85 mm Hg to ≥140/90 mm Hg for two reasons; first all epidemiological publications and databases used to develop the model defined hypertension as blood pressure of ≥140/90 mm Hg and second, because cur- rent European and U.S. guidelines use this definition as the treatment threshold for antihypertensive medication [15,30].