Study Design, Settings and Participants
We conducted a cross-sectional study between December 2021 and February 2022 in five different nephrology centers located in different cities across Turkey. All participant centers were tertiary care university hospitals. Patients older than 18 years of age with a diagnosis of ultrasound-based ADPKD were included in the study. (9) Patients who were unable to fill out the questionnaire or were on dialysis treatment were excluded from the study. Demographic data, serum creatinine, serum sodium, estimated glomerular filtration rates, and data on tolvaptan treatment were collected. Stage of ADPKD was defined according to Mayo clinic classification using MRI data. (10)
Survey Development and Data Collection
Thirst distress scale-heart failure (TDS-HF) included items related to the desire for water intake in contrast to thirst distress scale-renal failure (TDS-RF) which quantifies only the effect of water deprivation. The previous TDS developed for patients with heart failure and renal failure were used to quantify thirst distress due to water deprivation in contrast to the distress in ADPKD patients who are advised to drink abundant water. However, despite increased water intake, patients with ADPKD might also be prone to thirst distress when they are on tolvaptan therapy. In addition, either prescribed or tolvaptan-induced water intake might be associated with frequent urination or nocturia that may disturb the daily routines and quality of life of the patients. Patients might tend to avoid water intake to avoid frequent urination; in that case, especially in patients on tolvaptan therapy, thirst distress might increase.
Based on these facts, the items in the original TDS were modified for ADPKD through literature review, interviews with ADPKD patients, and considering patients’ experiences to develop a new questionnaire.
The new questionnaire was based on the TDS-HF developed by Waldréus et al. (6) The eight items of the original TDS-HF are rated on a five-point Likert scale, with a total score ranging between 8 and 40. A higher score indicates more thirst distress. The author of TDS-HF, Nana Waldréus, granted permission to modify the instrument for patients with ADPKD. (6)
The following changes were made:
a. We excluded one item since the study population are usually advised to drink water as much as they can.
‘I am so thirsty I could drink water uncontrollably’.
b. We added five new items to assess the factors that promoted or limited water intake.
-Factors promoting water intake:
‘If I don’t drink enough water or liquid, I get headaches’,
‘When I am thirsty and I cannot get enough liquid, I get nervous’, and
‘When I am thirsty, I cannot work well and I lose my concentration’.
- Factors limiting water intake:
‘I cannot get enough liquid to avoid frequent urination in the daytime’,
‘I have to wake up at night and cannot sleep well because of nocturia during nighttime’.
A total of 12 items regarding TDS-PKD were rated on a five-point Likert scale. Thus, the total score ranged between 12 and 60.
Following the modification of the scale, the English form was translated to Turkish separately by two bilingual medical experts; a nephrologist and an internist. Subsequently, the translated Turkish form was back-translated by a bilingual English translator, specialized in medical translations. Thereafter, all original, translated, and back-translated forms were evaluated by a panel of bilingual experts. The panel was composed of two participants who performed the first translation, one who performed the back translation, and two additional nephrologists who are specialized in the care of ADPKD patients. The final version in Turkish was constructed by the agreement of all participants. The translations were made according to the World Health Organization (WHO) guidelines on translation. (11)
Thirst intensity was measured using a visual analog scale (0: no thirst to 10: severe thirst). (6) The patients were requested to rate the severity of thirst from zero to 10 points. Zero refers to ‘I don’t feel thirsty’ and 10 refers to ‘the feeling of thirst is very severe’. The VAS score was classified as follows; mild (0-3), moderate (4-6), and severe (7-10). (6, 12)
We collected data using an electronic survey created by the SurveyMonkey© platform. The survey was filled out by the patients.
The data are presented as mean values and standard deviations (SD) and median [minimum-maximum]. Sampling adequacy was measured with the Kaiser-Meyer-Olkin (KMO) test, while Barlett’s test of sphericity was used to test the appropriateness of factor analysis. Exploratory factor analysis was conducted to reveal the validity and the factor structure of the questions in the questionnaire. Principal components were extracted using principal component analysis and varimax rotation method with Kaiser normalization. In factor analysis, the rule that eigenvalues greater than 1 was used to decide on the number of factors. Internal consistency of the TDS-PKD was evaluated with Cronbach's alpha coefficient and homogeneity of the questions with Hotelling's T-squared test. The correlation matrix was used to analyze inter-item correlations. The correlation between factor scores and the VAS scale was evaluated with Spearman’s correlation analysis. All statistical analyses were performed using IBM SPSS version 21 (IBM Corp., Chicago, IL, USA) and R software (version 4.0.2).