A total of 302 patients participated in the study. All patients received haemodialysis treatment in three out-of-hospital haemodialysis units in the Community of Madrid during the period between January 2014 and December 2017. The inclusion criteria for this study were being over 18 years of age, having the diagnosis of ACKD and undergoing regular haemodialysis, and having completed a full psychological and social evaluation, which is part of the reception protocol of the participating units. The exclusion criteria were having an intellectual disability, cognitive impairment, not having a sufficient understanding of Spanish or not having completed a full psychological and social evaluation. Of a total of 406 eligible patients, 61 patients were excluded because they did not meet the inclusion criteria and 43 were considered lost due to incomplete data.

All the data used for this study were collected through the process of a medical, social and psychological evaluation that was carried out routinely at the site where the research was performed, and were used retrospectively for this article. This was a non-experimental, cross-sectional and correlational study that measured the following psychological variables: (1) physical and mental HRQoL; (2) anxiety; and (3) depression. In addition, sociodemographic variables collected through semi-structured interviews were evaluated. The medical data were extracted from the medical records of the patients participating in the study.

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  12-Item Short Form Health Survey (SF-12).16 Spanish version validated by Alonso, Prieto and Antó.17 The SF-12 survey is an instrument used for HRQoL evaluation. It consists of 12 items selected by multiple regression from the items of the 8 dimensions of the 36-Item Short Form Health Survey (SF-36).18 The SF-36 health survey is one of the world's most widely used generic instruments for evaluating HRQoL.17,18 The SF-12 yields scores that correspond to the Physical Component Summary (PCS) and Mental Component Summary (MCS). It is answered using Likert scales of between two and six points depending on the item. The scale has an internal consistency greater than 0.70 (Cronbach's alpha)19 and adequate construct validity18. In this study, the overall internal consistency of the survey was 0.808, 0.715 for the physical component and 0.727 for the mental component.

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  Goldberg Anxiety and Depression Scale (GADS).20 Spanish version validated by Mortón et al.21 This scale consists of two subscales, one to evaluate anxiety and the other for depression, with nine items each, and with dichotomous responses (Yes/No). The first four questions of each subscale are mandatory, and the other five depend on the responses to the previous questions (in the anxiety subscale, questions five to nine are asked if the patient answers "yes" to at least two of the four initial questions, and in the depression subscale if the patient answers "yes" to at least one). It is considered a scale for healthcare and epidemiological use, useful as a guide for the detection of anxiety, depression or mixed problems. Goldberg et al. (1988) proposed a cut-off point of ≥4 for the anxiety scale and ≥2 for the depression scale. These cut-off values have demonstrated a sensitivity of 83.1% and a specificity of 81.8%, as well as a positive predictive value of 95.3% in the Spanish population.21 In this study, the internal consistency of the overall scale was 0.782, while it was 0.654 in the anxiety subscale and 0.705 in the depression subscale.

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  Sociodemographic questionnaire. A document designed ad hoc that included gender, marital status, living arrangements, level of education, employment status and legal recognition of the degree of disability and dependency. These data were collected in the evaluation interviews that were conducted during routine healthcare carried out at the site where the patients were receiving dialysis treatment. The degree of disability is expressed as a percentage and constitutes individual recognition of a physical, mental, intellectual or sensory limitation, to which other social factors that hinder the social integration of the person are added. For haemodialysis patients, the degree of disability corresponds to a mild-moderate degree and the percentage is between 50% and 70%.22 Dependency is expressed in degrees and constitutes recognition of a situation of permanent loss of physical, mental, intellectual or sensory autonomy, which requires the help of other people to perform the basic activities of daily living (ADLs), either due to age, illness or disability.23 This study only considered the legal recognition of the degree of disability and dependency.

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  Clinical questionnaire to collect the patient's medical variables. This included the aetiology of ACKD, characteristics of entry into haemodialysis, time (months) on haemodialysis, weekly hours of treatment, status concerning the transplant list, number of previous kidney transplants, age-adjusted Charlson comorbidity index (ACCI)24 and evaluation of physical activity. This last item was evaluated by a question about the level of physical activity that the person performs, and was answered using a Likert scale with the following options: frequently (does regular physical activity or walks at least three days/week for a period of at least an hour), sometimes (occasional physical activity or walks fewer than three days/week and for less than an hour) and never (reports not doing any type of physical exercise).

The patients were individually evaluated between January 2014 and December 2017. Regarding informed consent, exceptionally, specific consent was not requested for this study, since it is a retrospective study that uses data obtained in the psychological and social assessment that is part of the healthcare process that is carried out routinely for all patients receiving dialysis treatment at the study sites. The size of the sample (302) and the period analysed (four years) made it very difficult (or even impossible in the case of transfers, transplants or deaths) to obtain consent for a large number of patients in the sample. However, this study was approved by the Independent Ethics Committee of the Hospital Universitario Fundación Alcorcón [Alcorcón Foundation University Hospital] (IEC-HUFA), the referral hospital of one of the dialysis sites participating in the study. The IEC was duly informed of the lack of informed consent and, understanding the reasons for this, the committee approved the conduct of this research based on the data already collected in the patients' medical records.

First, the descriptive statistics of the variables evaluated were obtained. Subsequently, the Kolmogorov-Smirnov normality test was performed. If the data followed a normal distribution, parametric tests were used; otherwise, their non-parametric version was used. To study the relationship between continuous variables, Pearson correlations were performed, while to study the differences in anxiety, depression and HRQoL scores as a function of categorical variables, Student's t-tests or one-way ANOVAs were performed. Once the variables significantly related to HRQoL in this study were known, a structural equation model called Path Analysis with Latent Variables (PALV) was performed with the aim of exploring the degree to which the different variables evaluated contributed to predicting the level of HRQoL. The PALV entails an extension of the multiple regression analysis since it allows us to not only find out to what degree various dependent variables (in this case comorbidity, depression, anxiety, physical activity, etc.) help to predict a dependent variable (in this case HRQoL), but also how the different predictors relate to each other, directly and indirectly influencing the dependent variable.25 However, it is important to note that the model does not allow causality to be inferred in itself, but rather facilitates understanding regarding to what degree a possible causal hypothesis is compatible with or fits the data obtained.26 To evaluate the degree of fit of the PALV, the Chi square absolute fit index divided by degrees of freedom (χ2, χ2/df), the Goodness of Fit index (GFI), the Incremental Fit Index (IFI) and the following non-central tendency indices of fit were used: Comparative Fit Index (CFI); Root Mean Square Error of Approximation (RMSEA); Standardised Root Mean Square Residual (SRMR), as well as the criteria for acceptance or rejection of the model described by Hair, Black, Babin, Anderson, & Tathan (2010)27 (χ2/df ratio <5; SRMR<0.08; RMSEA and SRMR<0.08; GFI, CFI and IFI>0.90).

HRQoL scores on the SF-12 Health Survey, on a scale of 0–100, were 45.03 (SD=14.22) on average for the Physical Component Summary (PCS) and 58.73 (SD=12.79) for the Mental Component Summary (MCS). When comparing the values found in the sample for the HRQoL components, the results were significantly lower than the population mean (mean PCS and MCS reference score for the Spanish population 50)18 for the PCS (t=−4.96; p<0.001) and significantly higher for the MCS (t=11.87; p<0.001) (Table 2).

The mean score for anxiety was 1.54 (SD=2.14) and 1.54 for depression (SD=2.11). Women showed higher levels of anxiety (p=0.014) and depression than men (p=0.045) (Table 2).

None of the other sociodemographic variables evaluated was related to HRQoL, anxiety or depression except for age, which showed a statistically significant, inverse and weak correlation with physical HRQoL (r=−0.122; p=0.034).

The data showed a significant, inverse and weak correlation between physical HRQoL and comorbidity. Statistically significant, positive and weak correlations between HRQoL (both dimensions) and physical activity were also found. No statistically significant differences were found regarding HRQoL, anxiety and depression with regard to the rest of the medical variables evaluated (cause of kidney disease, form of entry to haemodialysis, time on haemodialysis, etc.) (Table 3).

Anxiety and depression were more closely related to the mental dimension of HRQoL than to the physical dimension. Depression showed higher correlations with both dimensions of HRQoL than anxiety (Table 3).

The results so far have demonstrated that the only variables related to HRQoL are physical activity, depression, anxiety and comorbidity. To study the joint effect of these variables in predicting HRQoL, and considering the existing correlation between anxiety and depression, a PALV was performed. In this model, only items one to four of the anxiety and depression subscales of the Goldberg Anxiety and Depression Scale questionnaire were included, because they were the only items that all the patients answered, and the PALV does not allow for the inclusion of variables with missing values in the model. Fig. 1 shows this model, with the regression weights and the percentage of variance explained in HRQoL. The model indices of fit are shown at the bottom of Fig. 1.

Fig. 1.

Path Analysis with Latent Variables for predicting quality of life and its indices of fit.

Note: 1=Goodness of Fit Index; 2=Incremental Fit Index; 3=Comparative Fit Index; 4=Root Mean Square Error of Approximation; 5=Standardised Root Mean Square Residual. The model was calculated with a sample of 283 patients, after eliminating from the sample patients with missing data for any of the variables included in the model. AG_1 to AG_4 and DG_1 to DG_4=items 1–4 of the anxiety and depression subscales, respectively, of the Goldberg Anxiety and Depression Scale.

(0.26MB).

Overall, 42% of the variance in HRQoL can be explained from the variables included in the model. Depression was the variable with the highest weight in the prediction (−0,71, p=0.002), followed by physical activity (0,12, p=0.044). Neither anxiety (0.10, p=0.628) nor comorbidity (-0.08, p=0.176) contributed significantly to the prediction of HRQoL (Fig. 1).

Regarding the model indices of fit, all were found to be within the acceptance limits, as shown in Fig. 1, and it can be concluded that it is well estimated.