Aspects of health-related quality of life : Associations with psychological and biological factors, and use as patient reported outcome in routine health care

Background Health-related quality of life (HRQoL) is increasingly recognised as an important patient-reported outcome in health care research. However, the use is still restricted and several questions remain about the value and feasibility of using measures of HRQoL in routine health care. The general aims of the thesis were therefore to increase the understanding of these issues by studying 1) associations of HRQoL with psychological and biological factors, 2) comorbidity adjustments of HRQoL measurement results, and 3) the patient-perceived value and feasibility regarding the use of measures of HRQoL as patient-reported outcome in routine health care. Methods Three different data sets were used; baseline data (questionnaire, anthropometric, and biological) from the ongoing Life conditions, Stress, and Health Study (n=1007, papers I and II), data from a population survey from the County Council of Östergötland in combination with data from two national Swedish registries, the National Inpatient Register and the Causes of Death Register (n=6086, paper III), and data (questionnaire) from the multicentre Swedish Health Promoting Hospitals Network Health outcome assessment project (n=463, paper IV). The HRQoL measures used were the SF-36 and the EQ-5D. Statistical methods include variance, correlation and regression analyses. Results Psychological resources (Self-esteem, Sense of Coherence, and Perceived Control) as well as psychological risk factors (depressive mood) were found to relate independently to HRQoL (SF-36) in the expected directions (positive relations for resources and negative relations for risk factors), but with fewer sex differences than expected (Paper I). Low HRQoL (SF-36) was found to relate to higher levels of inflammatory biological factors (C-reactive protein, Interleukin-6, and MatrixMetalloProteinase-9), and, especially regarding Interleukin-6, many association remained significant, though attenuated, after adjustment for factors of known importance to HRQoL (age, sex, disease, lifestyle and psychological factors) (Paper II). A new comorbidity index, the Health-related Quality of Life Comorbidity Index (HRQL-CI), explicitly developed for use in HRQoL outcomes studies, showed higher explanatory power (higher R2 values) than the commonly used Charlson Comorbidity Index (CCI) regarding impact of comorbidity on HRQoL (SF-36 and EQ-5D). However, regarding mortality the CCI discriminated better between those who died within a year from answering the HRQoL questionnaires, died within ten years, or who were still alive after ten years. This result is in line with the CCI’s original purpose as a mortality predictor. Using morbidity data from mandatory, highly valid national health data bases was found to be useful in a large study of this kind, where using data from medical records might be impractical. (Paper III). Using measures of HRQoL as patient-reported outcome measures in routine health care was regarded as valuable by the majority of the patients in the Health outcome assessment project. A new concept was introduced, respondent satisfaction, and the respondent satisfaction summary score was in most cases equal, i.e. SF-36 and EQ-5D were found to be quite similar regarding the cognitive response process (understanding and responding to the items in the EQ-5D and the SF-36) and patient-perceived content validity (if EQ-5D and SF-36 gave patients the ability to describe their health in a comprehensive way) (Paper IV). Conclusions The four papers investigated different aspects of HRQoL that are important for the implementation of the use of measures of HRQoL within the health care system. In conclusion, 1) the use of measures of HRQoL to identify patients with low HRQoL for further health promoting interventions might be supported on a psychological (psychological resources are related to better HRQoL) and biological basis (low HRQoL being an important sign of increased biological vulnerability), 2) a comorbidity index specifically aimed to adjust for comorbidity in patient HRQoL outcomes studies was found to be valid in a normal population (that might serve as a reference population in future studies), and 3) patients perceived the use of measures of HRQoL to be valuable and feasible in routine health care, and questionnaire length and ease of response were not found to be crucial arguments in the choice between SF-36 and EQ-5D. Hence, in their own way, they all and together, contribute to removing obstacles in the implementation process of using patient-reported outcome measures in the health care system for quality improvement.