Worldwide, more than 20,000 kidney transplantations after living donation are performed each year (1). In Germany, 2,195 kidney transplantations were done in 2015, of which, 645 (29.4%) were from living kidney donors (2). In the same year, there were 7,961 transplantable patients on the waiting list showing the unfulfilled high demand for donor kidneys. The mean waiting period for kidney transplantation with deceased donor organs in Germany is estimated to be 6–7 years (2), but depends on the blood group of the recipients. For patients with blood group 0, the average waiting time is currently 9 years in Germany (3). Living kidney donation has become the gold standard treatment of end-stage renal failure. The benefits of kidney transplantation with living donor organs compared to deceased donor organs include pre-emptive transplantation, superior organ quality, longer graft survival, and improved event-free survival of the recipient (4).

Well-being following living kidney donation continues to be a concern and an important area of research. Even though recent studies have raised some concerns related to the long-term somatic safety of living donation (5, 6), experts agree that the long-term risks for the donor are generally low (7). Living donors are healthier with regard to somatic as well as psychological comorbidity than the general population, due to rigorous medical screening for kidney donor eligibility. This is supported by the finding that donors tend to have higher health-related quality of life (HRQoL) before donation compared to the general population (8). Studies indicate that shortly after donation during the early postoperative recovery period, donors have lower HRQoL with major changes in physical functioning and pain. HRQoL usually returns to baseline over time or remains slightly reduced compared to baseline, particularly for fatigue, but scores are still comparable to general population norms (8). Only a small group of donors report adverse psychosocial outcomes. The majority report no change or even an improved relationship with their recipient. Some donors experience an increase in self-esteem and a high degree of resilience, post-donate growth, and purpose in life (8–10). Almost all donors report that they would donate again supporting the living donation procedure (11). Thus, there is evidence that donors might even benefit psychologically from donation.

Little is known about the personality of individuals who chooses to consider living donation and if certain personality traits are common among living organ donors compared to the general population. One study investigated personality traits in 107 US living kidney donors, most of whom were 2–11 years after donation (10). They used the NEO-Five Factor Inventory (NEO-FFI) and found T scores (<45) in the low range for neuroticism and T scores (>55) for extraversion, agreeableness, and conscientiousness in the high range compared to age- and sex-specific population norms. The authors concluded that the donors in their sample showed a high degree of adaptive personality traits. However, the response rate was low, with only 16% of all kidney donors responding to the survey. It is perceivable that individuals with high agreeableness and conscientiousness might have been more willing to respond to a survey. Also, the cohort included 27% of kidney donors who were not part of the immediate family. Altruistic donors might have different personality profiles compared to donors with a close relationship to the recipients. German Transplantation Law does not permit altruistic donation and the personality profiles might, thus, be different in a German living kidney donors.

The aim of the study was to investigate personality traits in a large sample of German living kidney donors and to compare the results with a German norm population. In line with earlier studies, we expected to find more adaptive personality traits, specifically with regard to neuroticism, agreeableness, and conscientiousness. In addition, gender differences were investigated. Finally, correlations between personality traits and symptoms of depression, anxiety, and fatigue as well as the association with regret regarding donation were examined.

A total of 535 surveys were mailed to the selected living kidney donors. After numerous attempts, 315 were returned, for a response rate of 58.9% (Figure 1). Donors who did not return the survey did not differ significantly with regard to age [55.0 (SD 8.4) versus 55.9 (SD 8.0) years], sex (females 65.9 versus 64.1%), and relation to the organ recipient when compared with donors who returned the survey. However, years since donation differed significantly between participants and non-participants [8.24 (SD 5.2) versus 7.1 (SD 5.2) years; T = −2.297 (df = 477), p = 0.022].

Table 1 presents the demographic and clinical characteristics of the participants who completed the survey. Except for the relationship to the recipient, no characteristics differed between male and female donors. Male donors were more likely to have donated to a child (47.8%) whereas female donors more often donated to their spouse (44.1%) (Figure 2). Eighteen (5.7%) organ recipients had died. Of the 292 recipients who were alive (no information were available for 5 recipients), 20 (6.8%) had lost the donor’s kidney and 4 were on dialysis. Mean age at donation was 48.8 years (SD 8.8) ranging from 25 to 68 years [median 49 years (IQR 12)]. Years since donation ranged from 1 to 29 years with an average of 7.1 years (SD 5.2) [median 6 years (IQR 7)]. Overall, 239 (75.9%) donors reported no regrets at all whereas 73 (24.1%) reported at least some regret regarding donation. Of the latter 43 (13.7%) would likely donate again, 30 (9.6%) were unsure or would not choose to be a donor again, and 3 donors did not answer this question. 193 (61.3%) donors perceived their current relationship with the recipient as very good, 79 (25.1%) as good, 25 (7.9%) as neutral, bad, or very bad, and 18 did not answer this question. Finally, 69.9% donors described their own health as good to very good and 22.9% as moderate (Table 1).

T-scores for the five NEO-FFI dimensions were calculated for each participant. Compared to the German sex- and age-related population norms, the median values of the agreeableness T scores were above average (>55) in both male and female kidney donors. The median of the neuroticism T scores was below average (<45) in male donors and the median of the openness T scores was below average (<45) in female donors. All other T scores were in the average range (45–55) in both sexes. Overall, 49.4% (n = 154) reported neuroticism T scores below average and 51.3% (n = 160) reported agreeableness T scores above average. Male and female donors differed significantly on the neuroticism, extraversion, and openness T scores (Table 2; Figure 3).

Donors without any regret (n = 239) were compared with all other donors who reported at least some regret (n = 73). Donors without regret had significantly lower median neuroticism scores (Z = −3.973, p < 0.001) and significantly higher median values for extraversion (Z = −3.691, p < 0.001), agreeableness (Z = −3.555, p < 0.001), and conscientiousness (Z = −2.822, p = 0.005) compared to the remaining donors (Figure 4). These differences between groups were identified for both male and female donors with non-regreters showing more adaptive personality traits, which were frequently even below (neuroticism, openness) or above (agreeableness, conscientiousness) average levels in both sexes. 84.9% (n = 129) with neuroticism T scores below average reported no regret as opposed to 68.8% (n = 108) with T scores within the normal range or above average [χ² = 11.172 (df = 1), p = 0.001]. The respective percentages for agreeableness T scores were 83.6% (>55) versus 69.3% (≤55) [χ² = 8.849 (df = 1), p = 0.003].

We found no differences in personality profiles between genetically and emotionally linked donors (data not shown).

Symptoms of depression and anxiety were within the normal range and the average values were far away from the cutoffs of ≥10; however, 7.6% of the sample exhibited values above the cutoff on the anxiety scale and 10.2% on the depression scale (Table 3; Figure 5). Female donors had significantly higher depression and anxiety scores compared to male donors (Table 2); however, the percentage of patients above the cutoff score of 10 did not differ between sexes and were comparable to population values (16).

Scores on the 5 subscales of the MFI-20 did not differ between sexes (Table 2; Figure 5) and were similar to population norms. When comparing the mean values between the donors and a sample of 693 individuals aged 40–59 years from the general German population (20), effect sizes (Cohen’s d) for mean values were low, not exceeding 0.2. This was true for both sexes.

Except for openness, the NEO-FFI dimensions were significantly correlated with the levels of depression, anxiety, and fatigue. While neuroticism was negatively correlated, extraversion, agreeableness, and conscientiousness were positively correlated (Table 4). However, only for neuroticism the correlation coefficients were >0.5 (but <0.64) indicating a relationship of moderate strength. All other correlation coefficients were <0.5 indicating a weaker association.

Age of the respondents, age at time of donation, and duration since donation did not reveal significant associations with personality traits, levels of depression, anxiety, or fatigue (data not shown).

We identified specific personality characteristics in a large group of living kidney donors with higher than average levels of agreeableness in both sexes and lower than average levels of neuroticism in men and of openness in women. It is difficult to interpret the gender differences; however, the trend was in the same direction. These results were more pronounced in donors without any regret regarding donation. High agreeableness is characterized by good-naturedness, cooperativeness, and an overall prosocial orientation (forgiving, not demanding). Low neuroticism, on the other hand, is characterized by emotional stability and low vulnerability to stress. Overall, the results regarding agreeableness and neuroticism are similar, even though less pronounced, to the results of an earlier study in 107 kidney donors (10). Even though altruistic donation is not permitted in Germany and cross donation is hardly done, the personality profile resembles the profile found within the U.S. living kidney donors where these options are allowed. As opposed to this study, we did not find higher than average conscientiousness levels. As mentioned before, participation rate in the US study was only 16%, which may have resulted in a selection bias.

These results can be interpreted in different ways. More adaptive personality characteristics may influence the process of decision making and individuals with low neuroticism and high agreeableness might be more willing to donate. Specifically, agreeableness and neuroticism play an important role in social contexts and influence social interactions. Also, it is perceivable that individuals who describe themselves as altruistic and emotionally stable are more likely to successfully complete the screening process and to realize the living kidney donation. However, it remains unclear if individuals with a more adaptive personality profile are more willing to donate an organ or if there might be a selection bias of potential donors in the prescreening process with the acceptance of more “healthy” individuals as living donors. This is supported by a study of Erim et al. (11) who reported that living kidney donors who were excluded from donation after the screening process due to donor health related issues had significantly lower levels of resilience compared to eligible donors.

There is also an alternative explanation. Although personality is conceptualized as a stable dispositional behavioral trait, environmental factors have shown to influence stability and change of personality traits. This has been most extensively investigated for neuroticism (21). There is clear evidence from longitudinal studies that positive live events such as—among others—recovery from serious illness of a family member are associated with small but lasting decreases in neuroticism. Thus, the low levels of neuroticism in our male sample might be explained by a true and lasting shift in neuroticism caused by the improvement of the health of a close family member. Others have reported that over an 8-year period, changes of all five NEO-FFI personality dimensions were significantly associated with changes in different measures of perceived social support (22). There is also evidence that relationship satisfaction is not only associated with decreases of neuroticism but also with small and lasting increases in extraversion over time (23). In addition, studies have shown (24) that there seems to be a reciprocal effect in that decreases in neuroticism may evoke positive experiences, which might lead to a benign cycle. Low neuroticism and positive experiences may reinforce each other in daily life. This might not only be of benefit for the donor but also for the relationship between donor and recipient. However, to what extent and in whom donation might lead to persistent personality changes is currently unsettled and can only be answered in prospective long-term studies.

Overall, levels of fatigue were comparable to the general German population and to an earlier German study including 295 living kidney donors (20, 25). Also, levels of depression and anxiety were comparable to German norms (16). Compared to a similar study in a German cohort of 295 live kidney donors (25), the mean depression scores on the PHQ-9 were comparable with 3.9 (SD 4.1) in our study and 3.59 (SD 3.99) in Sommerer et al (25). In our study, 10.2% of the donors met the cutoff (PHQ-9 ≥ 10) for depressive disorder, which was somewhat higher compared to the 2.1% reported by Sommerer et al. (25) but was within the range of 5–23% summarized in a systematic review (9). Female donors reported higher depression and anxiety scores compared to male donors; however, the percentage of donors with values above the cutoff (≥10) did not differ between sexes. The finding of a lack of difference with population values is in line with the majority of studies investigating quality of life, fatigue, and mental health post-donation (8, 9, 25–27). However, as with somatic complications, comparisons with general population samples are biased, since there is strong evidence that living kidney donors are physically and mentally healthier than the general population (8). Kroencke et al. (26) reported better HRQoL in living kidney donors compared with the general population, but comparable scores compared with healthy controls prior to donation and 1-year post-donation. General population samples might skew results in favor of the donor cohort for both somatic complications (27) and psychological sequelae (26). Post-donation comparisons with general population samples might even hide a negative outcome.

More adaptive personality characteristics were significantly associated with lower levels of fatigue, depression, and anxiety. This was true for all NEO-FFI dimensions except for openness to new experiences. In a meta-analysis of 10 prospective cohort studies low extraversion, high neuroticism, and low conscientiousness were found to be associated with depressive symptoms both cross-sectionally and also longitudinally (28). Personality traits, specifically, neuroticism seem to be robust predictors of vulnerability not only for mental health disorders but also for physical illnesses (29) and even predict longevity (after controlling for putative confounders). It has been argued that the economic burden of neuroticism exceeds that of common mental disorders and those of somatic disorders (30, 31). Hence, an adaptive personality style, either already present prior to donation or developing after donation, might protect against further mental complications and contribute to stable psychosocial health following donation.

This study contains a large group (n = 315) of living kidney donors with an acceptable response rate of 59% compared to the only other study that used the NEO-FFI in a donor sample (16% in 10), which improves the generalizability of our results. In addition, the NEO-FFI allows the calculation of sex- and age-specific standardized T-scores, which facilitates comparisons with population samples.

Several considerations may limit the interpretation of our findings. It is a cross-sectional study, there are no baseline questionnaire data prior to donation available and we do not know if there were within-subject changes after donation. More than 30% of the donors have not responded to the survey and a social desirability bias cannot be excluded. More agreeable donors might have been more willing to participate in the survey. However, except for time since donation, there were no differences between participants and non-participants at least with regard to age, sex, and organ recipients.

Future studies should consider ethnicity and immigrant status when investigating personality dimensions in organ donors. Finally, there is evidence that empathic concerns might predict donation willingness (32). Even though the personality dimension agreeableness shows a high correlation with empathy (33), the constructs are not entirely overlapping. The role of empathy in organ donors has not been investigated in depth as yet.

The study was approved by the Ethics committee of Hannover Medical School (no 3252-2016) and the participants signed an informed consent.

MZ, KW, and FG designed the study and received funding. All authors contributed substantially to the acquisition and interpretation of the data. MZ and IP analyzed the data and MZ and MN wrote the first draft. All authors critically revised the manuscript and gave their final approval. All authors gave their final approval of the version to be published.

All authors declare that the research was conducted in the absence of any commercial or financial relationship that could be construed as a potential conflict of interest.