Kidney transplantation has a positive impact on survival and morbidity of patients with end-stage renal disease. Recently, there has been increasing attention to health-related quality of life (HRQoL) as an important consideration in evaluating the impact of kidney transplantation. Kidney transplant recipients have better HRQoL than transplant candidates maintained on hemodialysis 12, and they experience an improvement of HRQoL in the first months after transplantation 34.

The HRQoL in kidney transplantation can be evaluated using generic tools, such as the Sickness Impact Profile (SIP), the Nottingham Health Profile (NHP) or the Short Form 36 (SF-36) 5. Some disease-specific tools for evaluation of HRQoL in relationship to renal transplantation have been developed, including the Kidney Transplant Questionnaire 6, and the ESRD symptom checklist – transplantation module (ESRD-SCL) questionnaire 7. Also, the Kidney Disease-Quality of Life (KDQOL) questionnaire is commonly used 8910, although it was not developed specifically for the evaluation of transplantation.

To conduct studies on HRQoL outcomes in kidney transplant patients, it is necessary to adapt relevant questionnaires and tools to the appropriate language and assess the psychometric properties of the questionnaires in relevant populations. Based on content analysis and available documentation, we identified the ESRD-SCL as a feasible questionnaire for use in kidney transplantation, in particular to evaluate the effects of immunosuppressant medication 11.

The objective of the present study was to assess the reliability and construct validity of a Norwegian version of the ESRD-SCL in renal transplant recipients.

The characteristics of the 59 respondents are shown in Table 1. ESRD-SCL and SF-36 scores are shown in Table 2, including the percentage of respondents giving lowest (floor) and highest possible score (ceiling). The ESRD-SCL scores did not concentrate at the ceiling for any subscale. However, scores concentrated at the floor for the Limited cognitive capacity, Side effects of corticosteroids, and Increased growth of gum and hair subscales (Table 2). For the SF-36 scales role – physical 30% of respondents scored the lowest possible value (floor). There were marked ceiling effects on the SF-36 scales role – physical (40%), bodily pain (25%), social functioning (50%), and role – emotional (67%) scales (Table 2).

The Cronbach's α was high for all dimensions of the ESRD-SCL (α = 0.72–0.81), for the total scale (α = 0.94) (Table 2), and for the scales of the SF-36 (α = 0.80–0.91). In the test-retest the respondents (n = 48) completed questionnaires median 14 days apart (interquartile range 9 to 20 days). In the test-retest, the intraclass correlation coefficients for the different subscales of the ESRD-SCL ranged 0.87 to 0.95, and for the SF-36 from 0.83 to 0.95.

In the assessment of construct validity, the hypothesized associations between scales of the ESRDL-SCL generally were among the highest, largely confirming the hypothesis, although some of the other subscales also correlated well (Table 3). The correlations of the two scales measuring medication side effects with the SF-36 scales were among the weakest pairwise correlations.

Among the demographic and clinical variables, employment showed the highest correlation with most of the ESRDL-SCL subscales, although these correlations were all weak and <0.40 (Table 4). Increased growth of gum and hair, a typical side effect of ciclosporin, was moderately associated with a ciclosporin-containing immunosuppressive regimen. With the above exceptions, associations of the ESRDL-SCL subscales with demographic and clinical variables were weak or close to nothing, as hypothesized (Table 4).

Only the ESRD-SCL subscale Increased growth of gum and hair discriminated between patients with two different immunosuppressive regimens after adjustment for age, sex, and comorbidity (Table 5). Only the two SF-36 scales Role – physical and Bodily pain discriminated between patients below/above the median age in the multivariate model. On the ESRD-SCL subscale Side effects of corticosteroids, younger patients tended indicate more problems than those above the median age, although this difference was statistically not significant (Table 5). The SF-36 physical functioning scale was the only scale that discriminated between patient groups according to Charlson comorbidity index ≤2 vs. >2 (p =< 0.001). The ESRD-SCL subscales Limited physical capacity and Cardiac and renal dysfunction showed differences that were almost statistically significant (Table 5), however, we hypothesized that these scales were associated with the Physical functioning scale of the SF-36.

In this cross-sectional study, the Norwegian version of the ESRD-SCL demonstrated high internal consistency reliability for all six subscales, in line with the original German version (α = 0.76–0.85) 7. Furthermore the test-retest reliability over 2 weeks for all scales was excellent. Reproducibility for the scales of this questionnaire has previously only been assessed over 1 year in stable patients 7. It has been suggested that HRQoL instruments can be used for comparisons at group level if reliability is above 0.70 23. All subscales of both the ESRD-SCL and the SF-36 instruments had higher internal consistency reliability than this. For use at the level of the individual patient, a suggested minimum requirement for reliability is 0.90 while 0.95 is desirable 23 although perhaps too stringent 24.

The pattern of correlations between the two instruments largely confirmed hypothesized associations from literature review and item content analysis, hence supporting convergent and discriminant validity of the ESRD-SCL 25. Furthermore, the associations of the ESRD-SCL subscales with demographic and clinical variables were in line with expectations. The patients accepted the questionnaire well, as demonstrated by the high completion rates.

We found no difference in HRQoL between a tacrolimus-based and a ciclosporin-based regimen using the SF-36, and no systematic difference on the ESRD-SCL subscales except the Increased growth of gum an hear subscale, however our sample was small. Previous studies have reported comparable effects on global HRQoL of the two regimens, while Tacrolimus has tended to improved the disease-specific HRQoL 112627282930.

A previous study has reported lower scores, denoting less side effects, on the Side effects of corticosteroids dimension of the ESRD-SCL and more suffering in the Limited cognitive function and Increased growth of gum and hair dimension among the elderly 7. In the present study we noted a statistically nonsignificant tendency to lower Side effects of corticosteroids in the elderly, however there was no indication of a difference according to age in the Limited cognitive dimension or Increased growth of gum and hair dimension in the present study.

Some weaknesses of the study should be noted. This study was a cross-sectional study in one hospital with a limited sample size, and all patients were successful renal transplant recipients.

The questionnaire contains items intended to assess side effects of immunosuppressive medication. Hence, the questionnaire can be a useful supplement to other questionnaires in studies of kidney transplantation, in particular in studies of variations in immunosuppressive medication following transplantation.

In summary, we have demonstrated that the psychometric properties of the Norwegian version of the ESRD-SCL were satisfactory and in line with the German original. Hence, the questionnaire can be recommended for use in future studies. The present study was not designed to evaluate responsiveness, which should be assessed in a longitudinal study.

The author(s) declare that they have no competing interests.

KS participated in planning and design of the study, organization of data collection, performed the statistical analysis, drafted and revised the manuscript. RG participated in the planning and design of the study, organization of data collection, and critically reviewed the manuscript. Both authors read and approved the final manuscript.