1. Introduction

Kidney transplantation is the gold standard treatment for end stage renal disease.[1] Living kidney donation is the solution to the current shortage of deceased kidney donors.[2] Many studies have reported that living kidney donation has a low incidence of postoperative complications. Additionally, serious psychological sequelae are rare; in particular, the quality of life of living kidney donors is no different from that of the general population.[3] Nevertheless, it is still difficult to assert that kidney donation has no effects on kidney function, risk of cardiovascular disease or death, and health-related quality of life (HRQoL).[4,5]

HRQoL can be defined as “self-perceived well-being that is involved or influenced by disease or treatment” or ‘how well a person is functioning in one’s life and self-perceived wellbeing in physical, mental, and social health.[6] Therefore, HRQoL of living kidney donors is an important indicator that can measure the health outcome after donation.[1] Several studies for identifying the HRQoL and factors associating with the HRQoL of living kidney donors have been conducted.[7–9] A systematic review and meta-analysis showed that long-term HRQoL levels of living kidney donors were equal to those of the general population; however, living kidney donors with low psychological functioning before donation are most at risk of impaired long-term HRQoL.[7] Therefore, it is necessary to pay attention to the psychological factors and functions that affect the HRQoL of living kidney donors.[10]

Self-determination is one of the psychological factors that affect the quality of life.[11,12] Self-determination is the ability to set and achieve goals on your own through understanding yourself, and to modify and develop goals as needed.[13,14] According to the self-determination theory, self-determined behavior can induce intrinsic motivation, and maintenance of the effects induced by the behavior is easier.[13] Furthermore, highly self-determined individuals can perform positive self-determined behaviors that assist in maintaining their physical and mental health.[13,15] Kidney donation is a decision with self-determination and voluntariness[16,17] and living kidney donors are estimated to have high self-determination; however, little research has been conducted on the self-determination of kidney donors. High self-determination can have a positive effect on their HRQoL, similar to self-determination’s influence on the quality of life of kidney transplant recipients or individuals with intellectual disabilities[11,12]; studies on the relationship between self-determination and HRQoL of living kidney donors are severely lacking. Self-determination can be exercised when 3 innate psychological needs—competence, autonomy, and relatedness—are satisfied. Satisfying these 3 psychological needs can improve self-motivation and mental health, leading to well-being.[13] Therefore, identifying the competence, autonomy, and relatedness of living kidney donors and examining their effects on HRQoL may be necessary to find a method to enhance their mental health and maintain well-being.

The physical health status of living kidney donors can also affect their HRQoL[18]; for instance, donor nephrectomy causes a sudden loss of approximately 50% of the nephron mass, and the health status of healthy living kidney donors may change after kidney donation.[7,19] Health problems such as diabetes, hypertension, hyperlipidemia, nephritis, or chronic renal failure may develop after kidney donation.[20,21] Thus, the occurrence of diseases, including decreased renal function, may be related to the HRQoL in living kidney donors. When evaluating the physical health status of a living kidney donor, it is necessary to identify whether health recovery after donation has been achieved according to objective indicators such as disease and creatinine levels. The word “recovery” has incompatible meanings. For example, recovery of function is a partial or complete return to normal, or partial or complete physiologic activity of an organ after disease or trauma; it is also a way to live a fulfilling, hopeful, and contributing life, even if it is limited by illness.[22,23] Therefore, it is necessary to identify whether objective health status and perceived health recovery match well and whether perceived health recovery affects HRQoL.

As such, it can be assumed that the self-determination and physical health status of living kidney donors is related to their HRQoL.[18,19] As competence, autonomy, and relatedness of self-determination may play important roles in improving the mental health and well-being of kidney donors, we investigated the impact of these aspects on the HRQoL of kidney donors. In addition, unlike previous studies that measured the physical health status of kidney donors with objective measurements such as disease occurrence and kidney function,[20,21] this study included a subjective measurement, perceived health recovery after donation, to evaluate kidney donors’ physical health. And we examined whether objective and subjective measurements were consistent and whether their impact on the HRQoL of kidney donors was different. This study provides evidence that it is necessary to assess the physical health status of kidney donors using both objective and subjective indicators. Therefore, this study aimed to identify the physical health status, self-determination, and HRQoL of living kidney donors and investigate the relationship of self-determination and physical health status with the HRQoL, which is necessary to find ways to improve HRQoL.

2. Methods 2.1. Aim

The purpose of this study was to determine the HRQoL of living kidney donors and to investigate the relationship between self-determination, physical health status, and HRQoL.

2.2. Research design

This study used a cross-sectional and descriptive design to investigate the factors associating with the HRQoL of living kidney donors in South Korea.

2.3. Participants

Participants were living kidney donors who visited the outpatient solid organ transplant center at Seoul National University Hospital for regular post-donation physical examinations between November 1, 2019 and August 15, 2020. Participant were aged ≥ 18 years who understood the purpose of the study, agreed to participate in the study, and were able to understand and respond to the questionnaire.

The required sample size was calculated using G power 3.1.[24] The minimal sample size (n = 98) was calculated under the assumptions of a significant level of 0.05, an effect size of 0.15, and power of 0.80. A total of 120 living kidney donors agreed to participate in the study, but only 111 living kidney donors completed the questionnaire. Therefore, the overall response rate was 92.5%. Data from the 111 participants, a suitable sample size, were included in the final analysis.

2.4. Measures 2.4.1. General characteristics and donation-related characteristics

Participants’ general and donation-related characteristics were assessed using self-report questionnaires. Participants’ general characteristics included sex, age, marital status, religion, posttransplant occupation, income source, and monthly income. The donation-related characteristics were voluntariness of the donation decision, relationship of the donor to the recipient, and time elapsed since the donation.

2.4.2. Physical health status

Data on disease, medication for disease treatment, and kidney function (serum creatinine level) were obtained from medical charts to evaluate the physical health status at the time of the survey. Perceived health recovery after donation was assessed with the question, “Do you think you have returned to the state of health as before the donation?” The following responses were obtained: Yes or No.

2.4.3. Self-determination

Self-determination was measured using the Korean version of the Basic Psychological Needs Index developed by Deci and Ryan.[13] The tool was translated, modified, and verified for reliability and validity by Lee and Kim.[25] This tool consists of 18 questions that measure autonomy (regulating the autonomy of behavior), competence (fully using one’s ability), and relationships (interacting with others in a social context). This tool is measured on a five-point Likert scale (from 1–5); the higher the score, the higher the degree of self-determination. The Cronbach alphas were .87 for Lee and Kim study[25] and .90 for this study, indicating high reliability.

2.4.4. HRQoL

HRQoL was assessed with the Medical Outcomes Study Short Form 36-item Health Survey (SF-36),[26] which was modified by Nam and Lee.[27] The SF-36 comprises a physical summary and mental component summary. The physical component summary refers to “physical function,” “role-physical,” “bodily pain,” and “general health”; and the mental component summary refers to “vitality,” “social functioning,” “role-emotional,” and “mental health.” The Cronbach alphas were .70 for Nam and Lee study,[27] and .90 for this study, indicating high reliability.

2.5. Data collection

The study was conducted between November 1, 2019 and August 15, 2020 at the outpatient solid organ transplant center of Seoul National University Hospital. Data were collected from the living kidney donors using structured questionnaires and medical charts. The researchers explained the purpose of the study to participants and distributed the questionnaire to participants.

2.6. Ethical considerations

This study was performed after receiving approval from the institutional review board of Seoul National University Hospital (H-1909-151-1067). Before data collection, the researchers explained the purpose of the study, the benefits and risks of participating in the study, and the security of personal information associated with the study. In addition, participants’ voluntary participation in the study was guaranteed and discontinuance was possible at any time during the study. Written consent was obtained from all participants.

2.7. Data analysis

Data were analyzed using SPSS statistical software (version 26.0; IBM Corp, Armonk, NY). Participants’ general and donation-related characteristics, physical health status, self-determination, and HRQoL were analyzed using descriptive statistics. Differences in the HRQoL according to the general and donation-related characteristics, and physical health status of the participants were analyzed using the independent t test and analysis of variance. The Scheffé test was used for post hoc analysis. Correlation between the variables was examined using Pearson correlation coefficient. Multiple regression analysis was performed to analyze the factors affecting the HRQoL. Categorical variables such as perceived health recovery after donation and time since donation, were included as dummy variables. The significance level was set at P < .05.

3. Results 3.1. HRQoL according to the general and donation-related characteristics and physical health status

A total of 111 living kidney donors completed the questionnaire. Participant age ranged from 24 to 78 years, and the mean age was 54.8 ± 10.0 years. More than two-thirds (73.9%) of the participants had jobs, and some of them worked as teachers, professors, and civil servants. All participants voluntarily donated their kidneys. Most participants (86.5%) had serum creatinine levels in the normal range (≤1.4 mg/dL), ranging from 0.7 to 1.7 mg/dL. One-third (40.2%) of the participants had diseases such as hypertension, diabetes, or hyperlipidemia; less than half of the participants (42.9%) were taking drugs for disease treatment; and most participants reported that their health had recovered since the donation (82.1%) (Table 1).

Table 1 - Health-related quality of life according to the general and donation-related characteristics and physical health status (N = 111). Variables Categories n (%) Health-related quality of life Mean ± SD t or F (P) General characteristics  Sex Female 51 (45.9) 77.0 + 10.4 1.38 (.17) Male 60 (54.1) 80.1 ± 9.3  Age (years) <41 10 (9.0) 80.5 ± 9.6 0.25 (.86) 41 to 50 23 (20.7) 77.5 ± 10.8 51 to 60 43 (38.7) 78.9 ± 8.7 60 or higher 35 (31.5) 79.3 ± 10.9  Marital status Never married, divorced, widowed 15 (13.5) 80.4 ± 9.7 0.62 (.54) Married 96 (86.5) 78.7 ± 9.9  Religion Yes 64 (57.7) 78.2 ± 10.0 −0.81 (.42) No 47 (42.3) 79.8 ± 9.8  Employment Yes 82 (73.9) 79.6 ± 9.7 0.68 (.51) No 2 (1.8) 75.7 ± 12.8 House maker 27 (24.3) 77.3 ± 10.3  Income source Self 63 (56.8) 79.3 ± 10.1 0.11 (.90) Spouse 24 (21.6) 77.9 ± 10.6 Other 19 (17.1) 78.8 ± 9.7 Missing 5 (4.5)  Monthly income (dollars) <1700 19 (17.1) 77.3 ± 10.1 0.17 (.91) 1701 to 2500 24 (21.6) 77.9 ± 10.6 2501 to 3400 24 (21.6) 77.9 ± 10.4 3400 or higher 39 (35.1) 79.3 ± 9.4 Missing 5 (4.5) Donation-related characteristics  Donation decision Voluntary 111 (100.0) 78.9 ± 9.9 – Nonvoluntary 0 (0.0) –  Relationship of donor to recipient Family* 65 (58.6) 78.8 ± 10.2 2.37 (.10) Spouse 44 (39.6) 79.7 ± 9.9 Other unrelated 2 (1.8) 64.4 ± 11.0  Time after donation Up to 1a 24 (21.6) 74.5 ± 7.8 12.35 (<.001)
a,d < b,c More than 1 up to 5b 35 (31.5) 81.9 ± 8.3 More than 5 up to 10c 41 (36.9) 82.2 ± 9.0 More than 10d 11 (9.9) 67.1 ± 10.1 Physical health status  Disease† Yes 45 (40.5) 80.4 ± 10.9 −1.27 (.21) No 66 (59.5) 78.0 ± 9.1  Medication for disease treatment Yes 48 (42.9) 80.5 ± 10.6 1.04 (.30) No 63 (56.8) 78.0 ± 9.3  Creatinine (serum) 1–1.4 (mg/dL) 96 (86.5) 79.3 ± 10.1 1.01 (.32) >1.4 (mg/dL) 15 (13.5) 76.5 ± 7.7  Perceived health recovery after donation Yes 92 (82.9) 81.0 ± 8.7 5.50 (<.001) No 19 (17.1) 68.8 ± 9.1

SD = standard deviation.

*Family includes parent, child, sibling, and other relative.

†Hypertension, diabetes, or hyperlipidemia.

There was no statistically significant difference in the HRQoL according to the general characteristics of the participants. Regarding differences in the HRQoL according to the donation-related characteristics, there were statistically significant differences based on period since donation (F = 12.35, P < .001). For physical health status, there was a statistically significant difference in the HRQoL according to the perceived health recovery after donation (t = 5.50, P < .001). However, there was no difference in the HRQoL according to the objective physical health status, such as the serum creatinine level, disease, and medication for disease treatment (Table 1).

3.2. Levels of self-determination and HRQoL

The overall mean score for self-determination was 3.9 ± 0.4. The highest score was reported for autonomy and the lowest score was reported for competence. The overall mean score for HRQoL was 77.9 ± 10.8. Among the physical component summary of HRQoL, the highest score was reported for physical function; the lowest score was reported for general health. Among the mental component summary of HRQoL, the highest score was for role-emotional; the lowest score was for vitality (Table 2).

Table 2 - Levels of self-determination and health-related quality of life (N = 111). Variables Mean ± SD Min Max Range Self-determination 3.9 ± 0.4 2.2 5.0 1–5  Autonomy 4.0 ± 0.5 2.5 5.0 1–5  Competence 3.7 ± 0.6 2.0 5.0 1–5  Relatedness 3.9 ± 0.5 2.0 5.0 1–5 Health-related quality of life 77.9 ± 10.8 40.0 100.0 0–100  Physical component summary 77.1 ± 10.6 51.7 94.5 0–100  Physical function 91.9 ± 9.6 63.3 100.0 0–100  Role-physical 85.5 ± 16.3 30.0 100.0 0–100  Bodily pain 84.0 ± 17.5 40.0 100.0 0–100  General health 67.3 ± 13.9 40.0 100.0 0–100  Mental component summary 78.9 ± 12.4 44.0 100.0 0–100  Vitality 69.2 ± 14.3 40.0 100.0 0–100  Social functioning 85.1 ± 17.6 30.0 100.0 0–100  Role-emotional 87.1 ± 17.2 30.0 100.0 0–100  Mental health 79.7 ± 13.3 40.0 100.0 0–100

SD = standard deviation.

3.3. Correlation between self-determination and HRQoL

HRQoL showed statistically significant positive correlations with autonomy (R = 0.25, P = .007), competence (R = 0.24, P = .010), and relatedness (R = 0.27, P = .004) of self-determination (Table 3).

Table 3 - Correlation between self-determination and health-related quality of life (N = 111). Self-determination Autonomy Competence Relatedness r (P) Self-determination_autonomy 1 Self-determination_competence 0.47 (<.001) 1 Self-determination_relatedness 0.45 (<.001) 0.64 (<.001) 1 Health-related quality of life 0.25 (=.007) 0.24 (.010) 0.27 (=.004)
3.4. Factors associated with the HRQoL

According to the result of multiple regression analysis, factors associated with HRQoL of the participants were perceived health recovery after donation (β = 0.42, t = 4.86, P < .001), up to 1 year since donation (β = 0.33, t = 2.69, P = .008), more than 1 up to 5 years since donation (β = 0.52, t = 3.89, P < .001), more than 5 up to 10 years since donation (β = 0.53, t = 4.07, P < .001), and competence of self -determination (β = 0.23, t = 2.16, P = .033). The explanatory power of these variables was 43.3%. Among these variables, the most powerful factor associated with HRQoL was more than 5 up to 10 years after donation. The next most powerful factors associated with HRQoL were more than 1 up to 5 years after donation followed by perceived health recovery after donation, up to 1 year after donation, and competence of self-determination. The variance inflation factor values were all <10, with no multicollinearity. The Durbin–Watson value was 1.89, which was sufficient to satisfy the independence of the residuals (Table 4).

Table 4 - Factors associated with the health-related quality of life (N = 111). Variable (reference) B(SE) B t(P) Constant 40.41 (7.04) 5.74 Perceived health recovery after donation (No) 10.83 (2.23) 0.42 4.86 (<.001) Up to 1 year after donation (more than 10 years after donation) 7.90 (2.94) 0.33 2.69 (.008) More than 1 up to 5 years after donation (more than 10 years after donation) 10.92 (2.81) 0.52 3.89 (<.001) More than 5 up to 10 years after donation (more than 10 years after donation) 11.31 (2.78) 0.56 4.07 (<.001) Self-determination _autonomy 1.63 (1.66) 0.09 0.98 (.33) Self-determination _competence 4.09 (1.89) 0.23 2.16 (.033) Self-determination _relatedness −0.35 (2.04) −0.02 −0.17 (.87) R2 = .433, adjusted R2 = .394, F = 11.22, P < .001
4. Discussion

The aim of this study was to investigate the effects of general and donation-related characteristics, physical health status, and self-determination on the HRQoL of living kidney donors in order to find strategies to improve their HRQoL. Factors associating the HRQoL of living kidney donors were found to be perceived health recovery after donation, competence of self-determination, and period since donation.

Among the physical and mental component summaries of HRQoL, physical function and mental health had the highest scores, whereas general health and vitality had the lowest scores. These findings are consistent with those of previous studies on living kidney donors.[28,29] This finding shows that living kidney donors recover their physical function and mental health after donation and maintain a HRQoL which is comparable to the general population.[1,7] General health and vitality had the lowest scores, similar to the results of studies in the general population.[1,7] However, since some living kidney donors complain of fatigue after donation that can affect general health and vitality,[30] research is needed to identify the factors such as fatigue that can affect their general health and vitality.

The most influential factors associated with HRQoL of living kidney donors were time since donation, especially, more than 5 up to 10 years after donation, followed by more than 1 up to 5 years after donation and perceived health recovery after donation. This finding can be partly explained by the results of research showing that the HRQoL of living kidney donors returned to baseline at 3 to 12 months after donation.[7] Living kidney donors can feel tired enough to interfere with daily life, and most living kidney donors experience fatigue resolution only after approximately 6 months.[5] In other words, the recovery period after donation had an important influence on the HRQoL of kidney donors. Meanwhile, in this study, the HRQoL of kidney donors gradually increased until 10 years after donation, after which it decreased. It is presumed that the HRQoL of kidney donors gradually increased as the health status of kidney donors had recovered after donation[5,7] and the kidney donors had adapted to the changing situation after donation. However, few studies have been conducted on kidney donors’ health recovery adaptation, and changes in their HRQoL for long times. In the future, studies on kidney donors’ health recovery, adaptation, and changes in HRQoL should be conducted to identify the various causes of change in HRQoL.

“Perceived health recovery after donation” was also found to be powerful factor affecting the HRQoL of living kidney donors. This result is supported by a previous study which showed that subjective thinking about the impact of donation on their health affects the HRQoL of living kidney donors.[31] As HRQoL consists of subjective and multifactorial concepts, the patient’s view of their health status is important for the HRQoL.[32] In this study, SF-36, a tool used to measure the HRQoL of living kidney donors, was used to measure the participant’s health perception rather than the participants’ health level.[33] Therefore, subjectively recognizing that individuals’ health has improved after donation can have a significant impact on the HRQoL of kidney donors. In this study, while subjective data for measuring the physical health status (the perceived health recovery after donation) affected HRQoL, objective data (the serum creatinine level, disease, and medication for disease treatment) were not associated with the HRQoL of living kidney donors. This result shows that what the living kidney donors perceive as recovery after donation may not always match the objective physical conditions, such as disease and medication. These findings are considerably meaningful as most health care providers are more likely to pay attention to the objective physical health status, including the kidney function.[4] Living kidney donors can experience various problems such as fatigue, increased sensitivity to body sensations, difficulties in adapting to the new body situation, and health concerns in addition to obje