**2. What is health-related quality of life (HRQOL)**

The concept of HRQOL has been around for many decades. In its constitution, the World Health Organization has defined health as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity" [10]. Quality of life (QOL) is a broad multidimensional concept that usually includes subjective evaluations of both positive and negative aspects of life [11]. It is often defined differently by variable groups and profes‐ sional societies. This adds to the difficulty of measuring QOL. Health constitutes an important component of QOL assessment. However, other parameters such as employment, education, housing, and family life are important contributors to the overall QOL. Cultural and religious beliefs and values also add to the complexity of assessing quality of life.

to uremia and improves many of the uremic symptoms such as anorexia, fatigue, and pruritus

Conventional hemodialysis (HD) is reasonably effective in removing small solutes by way of diffusion across membranes. However, middle molecules which are implicated in adverse outcome are poorly removed by such mechanism. Secondary analysis of the HD trial had suggested that survival may depend on clearance of such middle molecules [2]. Convective therapy is more effective in removing larger toxic middle molecules such as β2-microglobulin. High-volume online hemodiafiltration (OL-HDF) effectively achieves significant clearance of middle molecules. Such treatment has been shown to be beneficial in terms of lower risk of all-cause and cardiovascular mortality when compared to standard hemodialysis. Secondary analysis of initially negative clinical trials also demonstrated decreased mortality in recipients

Hemodiafiltration (HDF) combines diffusive and convective clearance of uremic solutes. It involves convection of large volume of fluid and infusing in the patient a replacement fluid that is ultrapure, sterile, and free of pyrogens. Utilization of online HDF where replacement fluid is prepared by further purifying dialysate fluid instead of manufacturer-provided solutions made it more practical and cost effective. It is believed that high-volume HDF by increasing clearance of middle molecules could potentially improve symptomatology, reduces morbidity, and may even improve survival [8]. These in turn could result in improved quality of life. Improved quality of life in hemodialysis patients has been associated with improved outcome. Analysis of data using the Kidney Disease Quality of Life Short Form (KDQOL-SFTM) obtained from 10,030 randomly selected hemodialysis patients from the USA, five European countries and Japan in the Dialysis Outcomes and Practice Patterns Study (DOPPS) demonstrated associations between HRQOL and the risk of death and hospitalization. Scores were determined for three components of HRQOL: (1) physical component summary (PCS), (2) mental component summary (MCS), and (3) kidney disease component summary (KDCS). Lower scores for the three major components of HRQOL were strongly associated with higher risk of death and hospitalization in hemodialysis patients, independent of a number of

Information on quality of life in patients receiving renal replacement therapy in the form of OL-HDF is scarce and inconclusive. The studies often involve small sample size and uses different methods of quantifying HRQOL. In this report, we will attempt to address HRQOL in patients under OL-HDF treatment by way of defining HRQOL, describing the most common instruments used to evaluate HRQOL and presenting brief summaries of clinical studies that

The concept of HRQOL has been around for many decades. In its constitution, the World Health Organization has defined health as "a state of complete physical, mental and social

investigated HRQOL in individuals receiving convective therapy.

**2. What is health-related quality of life (HRQOL)**

that have a negative impact on the quality of daily life.

of high-volume OL-HDF [3–7].

124 Advances in Hemodiafiltration

demographic and comorbid factors [9].

The World Health Organization defines QOL as "an individual's perception of their position in life in the context of the culture and value system where they live, and in relation to their goals, expectations, standards, and concerns" [12]. Assessment of quality of life should encompass not only the physical condition but also factors that have an impact on the individual's well-being such as social, economic, emotional, and psychological factors. Quality of life and health are closely related. Each can have a positive or a negative impact on the other depending on condition. Such a relationship is demonstrated by the notion that greater survival is associated with a higher-measured QOL [13, 14].

Assessments of HRQOL have evolved over the years to include aspects of overall quality of life that can be obviously shown to affect physical as well as mental health (MH) [15–17].

On the individual level, this includes physical and mental health perceptions and their correlates including health risks and conditions, functional status, social support, and socioe‐ conomic status. On the community level, HRQOL includes resources, conditions, policies, and practices that influence a population's health perceptions and functional status. The construct of HRQOL enables health agencies to legitimately address broader areas of public health policy in collaboration with a wider circle of health partners, including social service agencies and community planners.

HRQOL questions about perceived physical and mental health and function have become an important component of health surveillance and are generally considered valid indicators of service needs and intervention outcomes. Self-assessed health status also proved to be a more powerful predictor of mortality and morbidity than many objective measures of health [9].

The measurement of QOL should encompass many factors that affect a subject's well-being. It should include not just the physical aspect but also the social, emotional, intellectual, and cultural components that comprise daily life. According to this foundation, we can define an aspect of QOL as being health related. This health-related quality of life (HRQOL) represents the "physical, psychological, and social domains of health that are influenced by a person's experience, beliefs, expectations, and perceptions" [18]. Each of these domains can be meas‐ ured in two dimensions, objective assessments of functioning status and subjective perceptions of health as reported by the individual. The patient's subjective attitudes and expectations convert that objective assessment into the actual quality of life [10].

Within this context, health is defined as not only the absence of disease and infirmity but also the presence of physical, mental, and social well-being [11].
