Measuring health-related quality of life in cardiac patients: Table 1

This editorial refers to ‘Comparison of EQ-5D and 15D instruments for assessing the health-related quality of life in cardiac surgery patients’, by J. Heiskanen et al., on page 193. Assessment of health-related quality of life (HRQL) has become increasingly important in the management of cardiac patients. Many patients consider the quality of the additional life years gained just as important as length of life.1 Furthermore, there is evidence in cardiac patients that HRQL predicts adverse health outcomes including mortality and hospitalization, independent of more traditional risk factors.2–4 The goal of contemporary management, therefore, is not only simply to extend life expectancy but also to ensure a sufficiently high long-term HRQL, defined by emotional, social, and physical well-being.5,6 Several instruments exist and can be grouped as either generic or disease specific. Generic instruments are applicable across a range of target groups, allowing between-group comparisons and comparisons with the general population. Examples, included in Table 1, are the EuroQol instrument (EQ-5D), 36-item short form health survey (SF-36), 12-item short-form health survey (SF-12), 15 Dimensions instrument (15D), Health Utility Index (HUI), and the Quality of Well-Being scale (QWB). Disease-specific instruments, on the other hand, can only be used in specific disease groups preventing comparison with other disease groups and general population samples. Examples include HeartQoL, Seattle Angina Questionnaire, and Minnesota Living with Heart Failure questionnaire. Main characteristics of commonly used generic instruments (self-administered versions) Main characteristics of commonly used generic instruments (self-administered versions) Calculation of utility scores, based on responses to questions, is usually not possible with disease-specific instruments but is an important function of many generic instruments. Utilities typically rank between 0 (equivalent to death) and 1 (equivalent to full health). Utility as a measure of quality of life can be combined with measures of quantity of life (survival) to calculate quality-adjusted life years (QALYs). QALYs provide a quantitative measure of health gain and are used in cost-utility analyses by comparing the QALY gain with the additional cost of a given treatment. The outcomes of cost-utility analyses have become increasingly important in the assessment of treatment benefits and in decisions around treatment reimbursement. There is on-going debate about the value of generic HRQL measures and the extent to which different instruments are comparable in the information they provide.7–10 Utility scores provide a basis for comparing different instruments, but there remains concern about the effect of the instrument itself on the patient-reported outcome. Some generic instruments do not incorporate all relevant HRQL dimensions for a particular patient group. This may undermine the sensitivity of the instrument for capturing small changes between and within patients because the number of dimensions and answer categories determine the number of possible health states. Similarly, the content and focus of generic instruments may also influence their performance and comparability. Simple things like the reference point for self-reported symptom status—ranging from ‘today’, to ‘during the last 2 weeks’, ‘during the last month’, and ‘on a typical day’—can impact the comparability of different instruments as may the ‘valuation method’ used whether it be time trade off (TTO), standard gamble (SG) or, rating scales (RS). Several studies have focused on the comparison of different HRQL instruments in various disease groups. Evidence has shown that different instruments lead to different utility outcomes in the same individuals and this can have important implications for the decision-making process.10 Research on the interchangeability of different instruments and the most appropriate instrument to use in a given population is important for guiding researchers. In the linked paper, Heiskanen et al.11 compared the EQ-5D scores with the 15D scores in patients admitted for a coronary artery bypass surgery (CABG). Both pre- and post-operative HRQL scores were recorded. Pre-operative utility scores were significantly lower using the EQ-5D instrument but more importantly the QALYs gained after surgery differed significantly between measures with twice as much utility gain with EQ-5D. While EQ-5D appears appropriate for capturing poor health states, clinically meaningful differences were more often seen with the 15D tool which seems more sensitive to changes and does not share the substantial ceiling effect observed with EQ-5D (4.4% vs 31.9%). In neither instrument was a floor effect seen. The findings in this study are consistent with previously reported studies in cardiac patients12–14 and other patient groups.9 Not only the differences in baseline utility scores, but especially the differences in overall utility gain pose a major issue, especially due to the impact on QALY gain and the resulting cost-effectiveness outcome.15 Cost-utility outcomes resulting from different instruments that are not comparable pose a real threat to the usefulness and credibility of cost-effectiveness analyses. At present there is no consensus about best or worst performing generic instruments for evaluating HRQL outcomes of interventions and treatments. Some instruments perform better in certain disease areas, or age groups and some gain preference for practical reasons, perhaps because they are less burdensome for the patient. Meanwhile, researchers need to provide transparent information about the tools they select to conduct their studies and to recognize that comparison of QALY outcomes between studies should usually only be done when the same HRQL instrument is used. There seems little doubt that HRQL assessments will feature increasingly in outcomes research and more studies like that reported in the linked paper11 will be needed to compare the different generic instruments on offer. D.D.S. is financially supported by the Research Foundation Flanders. Conflict of interest: none declared.