The global prevalence of Chronic Kidney Disease (CKD) has been consistently increasing with population aging and increased prevalence of chronic diseases such as hypertension, diabetes, and obesity. The reported worldwide prevalence of CKD is approximately 13.4% (11.7~15.1%) [1]. According to the CKD Surveillance System, the prevalence of CKD among those in their 30s has increased from 13.2% to 14.4% over the last decade and is predicted to reach 16.7% by 2030 [2]. The rising impact of CKD has been globally recognized as a serious public health problem with high medical expenses combined with a higher risk of end-stage CKD as well as comorbidities, including health complications and mortality [3, 4].

The optimal treatment of CKD plays a major role in disease management; however, since patients with CKD cannot expect full recovery, lifelong disease management is crucial [5]. Therefore, patients with CKD need to go beyond simply adhering to the treatment regimens prescribed by their physicians. They are required to directly participate in their treatment process and assume health maintenance responsibilities by engaging in self-care activities such as making healthy lifestyle changes and practicing health behaviors [6]. Consistent and effective self-care is important because patients at the pre-dialysis CKD stage are at an increased risk of health complications and accelerated progression to end-stage CKD [7].

The terms "self-care" and "self-management" have been used interchangeably in literature pertaining to CKD. Although there is no clear agreement on the definition, self-care refers to the activities involved in self-management [5, 8, 9, 10]. Self-care is defined as activities performed by people to maintain and improve their health via self-maintenance, monitoring, and management [11]. The World Health Organization (WHO) refers to self-care as an effective approach to improving the health status of chronically ill patients, and the first step is assessing one's knowledge, beliefs, and behaviors [12]. To provide individualized care to patients, it is essential to assess areas of self-care vital for patients with CKD, set appropriate goals, and provide relevant information and training [13].

Unlike other chronic diseases, patients with CKD are often diagnosed with multiple chronic diseases, including diabetes and hypertension, making self-care more complicated [14]. Although it is recommended that patients with CKD focus on treatment regimens and self-care behaviors based on the CKD stage, there are common self-care behaviors that all CKD patients should adhere to. Despite the importance of self-care behaviors in CKD [6, 9, 10, 11, 13], the self-care tools developed to date mainly target pre-dialysis [15] and dialysis patients with end-stage renal disease [16, 17, 18, 19], wherein various self-care activities such as diet and exercise [16, 19, 20], medication, and blood pressure monitoring [15] are measured together, thus, making it difficult to identify problematic self-care behaviors and develop individualized care plans. Therefore, these domains are not suitable for assessing individual self-care behaviours in patients with CKD at all stages.

In order to bridge this gap in existing research, researchers at Kaohsiung Medical University, Taiwan, utilized an extensive literature review and clinical experience to develop the Chronic Kidney Disease Self-Care (CKDSC) scale consisting of 16 items across five domains assessing self-care behaviors in patients with CKD at all stages of the disease. The five factors of the CKDSC scale are conceptual frameworks for measurement based on literature reviews on the self-care behaviors of CKD patients and the clinical experiences of nephrologists [21]. The CKDSC scale is not limited to any particular ethnicity or culture, type of dialysis, or CKD stage, and its validity has been verified in China and Taiwan [21, 22]. The current study aimed to develop the Korean version of the CKDSC (CKDSC-K) by translating the original version and verifying its validity.

The CKDSC-K scale was systematically developed in this study through forward and backward translation, expert CVI assessment, pilot study, cultural adaptation via cognitive debriefing, statistical validation, and finalization steps following guidelines on the translation, adoption, and validation of scales used in multicultural medical research in order to verify its validity and reliability [24].

In the item analysis, item 5, "I myself may change prescribed drug dosage", in the drug adherence domain, had a kurtosis of 18.24, indicating a non-normal distribution. The score for item 5 was 4.83, which was higher than previously reported scores of 4.65 and 4.61, indicating highly skewed responses [21, 22]. In the ITC analysis, the ITC coefficient (r) for item 5 was .24, not meeting the ≥.30 criterion [27]. Therefore, item 5 was removed from the scale. As response bias or ceiling effect may have occurred because the survey was conducted within a hospital, future studies using an anonymous online survey are suggested.

In addition, the construct validity and concurrent validity of the CKDSC-K were assessed. An EFA was performed on a scale with 15 items after removing item 5. The same five factors were extracted as those in the original scale. The variance explained by the items was evenly distributed between 8.8% and 18.5%. The cumulative explained variance was found to be relatively high (75.3 %). These values are close to the variance explained by each item and the cumulative variance explained (75.0%) was reported at the time of the scale's development [21]. In the CFA, Factor 4 in the smoking behavior domain had an AVE of .23 and CCR of .36, not satisfying the requirement for convergent validity [28, 29], although satisfying the criteria for discriminant validity. Thus, the scale is considered valid.

In the internal consistency assessment performed to verify reliability, Cronbach's α for factors 1 to 4 of the CKDSC-K was higher than .76. Cronbach's α for the smoking behavior domain was .40, lower than Cronbach's α of the same domain (.87) and the cut-off value (.70) in the original version [31]; therefore, reliability was not established for the smoking behavior domain. Of the two items in the smoking behavior domain, item 13 "I do not smoke every day" had an ITC of .23, indicating a low contribution to the scale but was not removed as it was deemed essential. This item was the most extensively discussed during the cognitive debriefing (refer to Section 2.4.3) and meetings. In the pilot test, participants tended to provide the opposite response to negative questions. This error was reduced by rewording the items into positive sentences. However, directly translating the English term "every day" to stay faithful to the original text resulted in a situation where participants who were intermittent smokers responded with a "no" to an item asking whether they smoked every day. The fact that the score of the item in question, which was 3.51 in a previous study, was 4.67 in this study, may indicate significance. Thus, it is necessary to examine the results of the CFA and internal consistency analysis after removing the word, "every day", and rewriting the item as "I currently smoke". Although direct comparison with previous results was difficult since previous studies have not reported the percentage of smokers [21, 22], only 10.0% of the participants in this study were current smokers, requiring reanalysis using data with more smokers. An additional analysis of self-care scores revealed significantly lower self-care scores for smokers than for those who used to smoke or those who never smoked, indicating that the smoking behavior domain and items adequately assess smoking-related self-care.

The average CKDSC score of the participants in this study was 3.56, lower than previously reported scores of 3.84 and 3.88 [21, 22]. Of the five domains (medication adherence, diet control, exercise, smoking behavior, and blood pressure monitoring), the diet domain had the largest score difference from previously reported scores. This may be because 67.0% of the participants in this study had stage 5 CKD, as opposed to only 22.3% and 24.7% in previous studies [21, 22]. A low-sodium diet with a limited intake of spicy or salty foods, as well as a controlled intake of water, is recommended for patients with CKD. A typical Korean diet includes salty or spicy soups and broths that contain a large amount of water. Thus, limiting water intake is difficult for Korean patients with CKD, who reported diet control as the biggest challenge in adhering to a treatment regimen because of deep-rooted dietary habits despite receiving diet education [15]. The items in the diet control and exercise domains of the CKDSC use adverbs of frequency such as "always" to assess self-care behaviors. Although using adverbs of frequency is a valid approach to assessing self-care behaviors given the importance of consistency in self-care behaviors, it is necessary to revise the CKDSC such that it uses precise frequencies instead of subjective terms, such as "never", "sometimes", and "often". In other words, adverbs of frequency must be replaced with exact frequencies after establishing linguistic, cultural, functional, and metric equivalence to confirm previous results [32].

The current study is meaningful in that it has developed a scale that helps not only HD patients but also patients with CKD to recognize the importance of self-care behaviors before undergoing HD so that they can self-assess and self-manage their self-care behaviors rather than having them assessed by a healthcare provider. However, since the participants were selected by convenience sampling from a single medical facility and the validity of the smoking domain of the instrument was lacking, additional verification and caution are required in interpreting the results of this study. Additionally, the impact of comorbidities such as diabetes and the duration of CKD diagnosis on self-care behaviors cannot be disregarded.

The CKDSC-K scale developed in the current study can be used to assess and monitor self-care behavior among patients with CKD at all stages of the disease. The CKDSC-K is a simple assessment tool that comprises 15 concise items that cover five essential self-care domains and can be completed within a short duration. Thus, it is highly likely to be used in various clinical settings. Based on the results, some robust recommendations for future research are suggested. First, repeated studies should recruit patients with CKD from several hospitals and data should be collected anonymously to avoid response bias. Second, a validation study targeting the smoker group is recommended to test the reliability and validity of the smoking factor of CKDSC-K. Although it is important to avoid changing the composition of the original scale or distorting the meanings of questions, it is important to repeatedly verify the validity and reliability of domains such as diet control-which is recognized as the most important aspect of CKD management-after ensuring functional and metric equivalence of the scale by tailoring it to the Korean cultural context.