CAPÍTULO TERCERO Peritación

The most common method used in cost of diabetes studies is the sum-all medical approach (11). However, by adopting this method, studies capture all healthcare costs regardless of whether they are associated with diabetes or not. Such estimates fail to identify service use that can be attributed diabetes and thus, do not provide useful or meaningful estimates to inform policy. The number of studies estimating the excess costs associated with diabetes has increased in recent years (11,85,86). The disease attributable methodology is also commonly used, although mainly in the USA. This method underestimates service use and costs associated with diabetes due to its inability to capture use that does not appear directly attributable to diabetes (92,93). For instance, mental health co-morbidities in people with diabetes increase health service utilisation (94). Due to its reliance on established quantifiable causal associations, disease-attributable methodology will not capture such excess service use. Furthermore, this method is reliant on robust and appropriately specified population attributable fractions which are not always available.

The use of the incremental cost approach yields the most accurate and policy-relevant estimates of the cost of diabetes as it allows for the identification of the excess costs attributable to the diabetes (11,92,93). This approach allows for the control of important confounding factors and thus the identification of the excess costs independently attributable to diabetes (11,92,93). However, consideration of appropriate covariates is essential. For instance, if the aim is to estimate total excess costs attributable to diabetes adjusting for the presence of macrovascular and microvascular complications will lead to an attenuation in costs and provide an estimate of the costs attributable to diabetes independent of the presence of complications. Few studies have applied the incremental costs approach to examine the cost of diabetes (11). Of the studies adopting this approach, many have focused on specific hospital-based samples or have used routine healthcare data

23 to estimate direct costs. These studies may result in an overrepresentation of people with diabetes and also people with diabetes-related complications. Furthermore, due to data availability constraints, many incremental cost studies control for gender and age only (95). Honeycutt et al. demonstrate that controlling for age and gender only can result in an overestimation of diabetes-related service use and costs (92). Worldwide, there is a lack of accurate, comprehensive and comparable estimates of costs attributable to diabetes (5). Valid and reliable incremental cost estimates for diabetes are required at a regional and country level to improve the accuracy of global cost of diabetes estimates (5,10). To date, the only estimate for the economic burden of diabetes in Ireland comes from the CODEIRE study published in 2006 (96). Using data from 1999/2000, CODIERE uses a sum-all medical approach for a hospital based sample of Irish adults aged over 30 years with diabetes. They do not estimate indirect costs.

Due to wide variations in methodologies, comparisons across studies are hindered (11). However, despite this, there are a number of commonalities across international studies that provide insight into the economic burden of diabetes. Hospital in-patient costs account for the majority of direct expenditure associated with diabetes, followed by medication costs (97–105). Diabetes complications have a substantial impact on both direct and indirect diabetes costs (106–109). The Cost of Diabetes in Europe – Type II (CODE-2) study reported that in patients with both microvascular and macrovascular complications, the total cost of management was increased by 250% compared those without complications (110). More recent estimates are similar. In Denmark, the majority of costs were incurred among patients with major complications in 2011 (106). In Poland, the direct cost of hospital complication treatment were more than five times the direct costs of hospital treatment of people without complications (109). In studies assessing the direct and indirect costs, the ratio between the two varies and with the inclusion of differing cost categories and different methodologies, comparisons are limited. However, it is evident that indirect costs account for a significant

24 proportion of diabetes costs. Global estimates report that 34.7% (95% CI: 34.7, 35.0) of the total economic burden of diabetes is attributable to indirect costs (5). This varied from 40.0% in high-income countries to 33.5% in low-income countries. Higher estimates have been reported in some European countries, with over half the costs attributable to indirect costs in the UK and Poland (107,109).

2.9.1 Rising costs of diabetes

Should previous trends in diabetes prevalence and mortality continue, it is estimated that by 2030, the global economic burden of diabetes will increase to $2.5 trillion (95% CI: 2.4, 2.6) (7). This translates to an increase in costs as a share of global GDP to 2.2%. Major increases in the proportion of GDP attributable to diabetes costs are predicted for all world regions, between 2015 and 2030.

While global projections estimate an inevitable increase in the economic burden of diabetes between 2015 and 2030, country-specific data, demonstrating increasing costs, is only available for a small number of high-income countries (7). Evidence of the increasing cost of diabetes is largely based on research in the USA (8,9,97,107,111). The economic costs of diabetes, calculated by the American Diabetes Association, increased by 26% in the five-year period 2012 to 2017 (8). The increase is driven by increasing numbers of people with diabetes but also rising costs of medical care per person with diabetes (9,97). In the USA, medical spending attributable to diabetes per person doubled between 1987 and 2011 (9). Furthermore, each additional year with diabetes increases annual medical expenditure (112). As mortality rates in people with diabetes decline and years lived with diabetes increase, this has implications for the future costs of diabetes.

Medication costs have been identified as the primary driver of increasing medical expenditure on diabetes (8,9). Over half the increase in medical expenditure is due to rising

25 prescription costs (9). It is suggested that the observed increase in pharmaceutical expenditure can be attributed to a combination of increasing diabetes prevalence, advancements in clinical guidelines advocating long-term glycaemic control and the upsurge of new expensive medical treatments (8–10). As of 2016, there were at new least 171 new drug therapies in development for the treatment and management of diabetes and its related complications (113). With an emphasis on maintaining glycaemic control, the number of classes of glucose-lowering drugs developed over the previous two decades has more than tripled (114). Novel and innovative treatments are expensive and concern has been raised about whether the benefits of these medications outweigh their significantly higher costs (115). While empirical data is scarce, it is predicted these treatments contribute to rising medication costs associated with diabetes and the continued advancement in diabetes- related medical technology will increase per capita medical expenditure per year (9,10,31,116).