Transformation of 5-D itch scale and numerical rating scale in chronic hemodialysis patients
© The Author(s). 2017
Received: 20 August 2016
Accepted: 4 February 2017
Published: 8 February 2017
Pruritus is a common and frustrating symptom in hemodialysis (HD) patients and 5-D itch scale is proposed as a reliable measurement of pruritus. However, information regarding 5-D itch scale categories is currently unavailable. We explored optimal cut-offs 5-D itching scale based on numerical rating scale (NRS) categories in HD patients.
Four hundred and nine HD patients in China Medical University Hospital in December 2014 were included and severity of pruritus was estimated using NRS and 5-D itch scale. The association of NRS and 5-D itch scale was analyzed by linear regression. The optimal cut-offs for 5-D itch scale based on NRS categories were generated.
The average NRS was 3.4 ± 3.0 and the average 5-D itch scale was 10.9 ± 4.8. The 5-D score was strongly correlated with the NRS: r = 0.831 (p < 0.001). NRS = −2.31 + 0.52 × (5-D scale). The averages of 5-D scales were 6.4 ± 1.5, 9.6 ± 2.2, 13.1 ± 3.2, 15.7 ± 4.4, 19.5 ± 4.4 for no, mild, moderate, severe, and very severe pruritus based on categorized NRS. A 5-D itch scale categories were proposed, ≤ 8 for NRS = 0, 9–11 for mild pruritus, 12–17 for moderate pruritus, 18–21 for severe pruritus and ≥ 22 for very severe pruritus.
Categories for the 5-D itch scale were proposed based on the measurements of pruritus severity in HD patients. This information provides a simple solution that enables transformation between the 5-D itch scale and the numerical rating scale.
Keywords5-D itch scale Hemodialysis Pruritus Numerical rating scale
Summary of measurements of pruritus in the literature
Visual analogue scale (VAS), numerical rating scale (NRS), and verbal rating scale (VRS)
5D itch scale, four-item questionnaire, itch severity scale, pruritus grading system
Measurement of scratching episodes
Measurement of limb movements
Imaging of brain activity
Measurement of itch threshold
Scales assessing the psychosocial condition of the patient related to itch
ItchQoL, Dermatology Life Quality Index and Beck’s Depression Inventory
Multidimensional scales not only access pruritus intensity but measure the impact of pruritus on patients’ quality of life. Commonly used multidimensional scales include the pruritus grading system , the 5-D itch scale , and the itch severity scale . The 5-D itch scale was published in 2010 and was validated with Numerical rating scale (NRS) in individuals with human immunodeficiency virus, skin, liver, or kidney disease . The 5-D itch scale, sensitive to the changes of pruritus with time, is a brief, single paged, multidimensional quantification of pruritus. NRS, an unidimensional scale, which may be the most widely used is a validated measurement of UP in HD patients [1, 4, 6]. Pruritus intensity measured using NRS can be categorized into no (0 point), mild (1–3 points), moderate (4–6 points), severe (7–8 points), and very severe pruritus (≥9 points). However, information regarding the 5-D itch scale categories on uremic pruritus is currently not available. The aim of the study is to investigate the 5-D itch scale categories based on NRS categories in HD patients. The information found will enable comparisons of the pruritus intensity and prevalence of pruritus among studies using different score systems. This information would make contribution to bioinformatics researches.
All patients who received HD for more than 3 months and signed the inform consent in China Medical University Hospital were enrolled. Patients were excluded if they were younger than 20 years old or were not able to sign their own consent for any reason. The severity of pruritus was measured using a 0-to-10 NRS (0 = no pruritus, 10 = maximal pruritus)  and the 5-D itch scale . NRS categories were defined as 0 for no pruritus, 1–3 points for mild pruritus, 4–6 points for moderate pruritus, 7–8 points for severe pruritus, and ≥ 9 points for very severe pruritus . A severity of pruritus more than moderate pruritus was considered as symptomatic pruritus (NRS ≥ 4). The causes of kidney disease were diagnosed by the primary care physician of nephrology at the initiation of HD. Patients’ serum calcium and phosphorus were measured in the same month when the pruritus was measured and their intact parathyroid hormone (iPTH) and Kt/V were measured in 3 months after or before the pruritus was measured.
A descriptive analysis was performed as appropriate: median and interquartile range in the case of non-parametric variable and mean and standard deviation in the case of parametric distributed variable. Analysis of variance, Mann–Whitney U test, t-test, or chi-square test for categorical variables were performed according to standard indications. The association of 5-D itch scale and NRS was analyzed using linear regression. The receiver operating characteristic curve of the 5-D itch scale in association with symptomatic pruritus (NRS ≥ 4) was generated. All analyses were performed using IBM SPSS Statistics for Windows, Version 22.0 Armonk, NY: IBM Corp and a p < 0.05 was considered statistically significant.
Characteristics of all patients
N = 409
Causes of kidney disease
Numerical rating scale
5-D itch scale
Statistics of 5-D itch scale according to numerical rating scale (NRS)
5-D itch scale
Mean ± SD
No pruritus (0)
6.4 ± 1.5
9.6 ± 2.2
13.1 ± 3.2
15.7 ± 4.4
Very severe (≥9)
19.5 ± 4.4
Categories of 5-D itch scale compared to numerical rating scale categories
Numerical rating scale
n = 100
n = 133
n = 106
n = 39
n = 30
5-D itch scale
≤8 n = 141
9–11 n = 110
12–17 n = 109
18–21 n = 32
≥22 n = 16
In this cross-sectional study, we purposed 5-D itch scale categories based on their correlation with NRS categories of pruritus in HD patients. Information obtained from this study may enable an easy transformation between 5-D itch scale and NRS. The prevalence of pruritus is 43% using NRS (≥4) in this population and this prevalence is similar to that reported in the previous studies [2, 13]. The prevalence of pruritus is slightly lower (38%) when the 5-D itch scale with a cut-off of 12 points is applied. There is no truly “no pruritus” in the 5-D itch scale and the 5-D itch scale is 7.5 points higher than the NRS. A 5-D itch scale less than 8 points may be equal to NRS = 0. In addition, the prevalence of pruritus is lower when a cut-off of 12 points is used in the 5-D itch scale. A cut-off of 10 points of 5-D itch scale results in a close percentage of patients with pruritus defined by NRS ≥ 4. As shown in Table 3, 26.4% patients have higher pruritus intensity using NRS but have lower pruritus intensity in the 5-D itch scale. This might suggest over-estimation of pruritus in NRS. The NRS can be obtained in 10 s and this is the major advantage of NRS. It usually took one to two minutes to complete the 5-D questionnaire in most patients. The upper arm and forearm are the most common locations of pruritus in HD patients and most of the pruritus the tape used during HD. There are good correlations (0.88–0.92) between NRS and each domain of the 5-D itch scale. The 5-D itch scale provided detailed assessments on the distribution of pruritus and the effect of pruritus on quality of life. Some patients may report a higher NRS when they have the 5-D questionnaire before NRS but this difference is not statistically significant.
We also investigated factors associated with uremic pruritus, but we did not find a significant association of pruritus with patients’ age, gender, causes of kidney disease, calcium, phosphorous, Kt/v, and iPTH. Prior to the study, we suspect that patients with diabetes as the primary kidney disease may be associated with pruritus. The prevalence of uremic pruritus (44%) in patients with diabetes as their primary kidney disease was similar to the prevalence (42.2%) of non-diabetic patients. Diabetes was not associated with higher NRS and 5-D itch scale in linear regression, either.
There were some potential limitations of this study. First, the cut-offs of 5-D itch scale were determined using the equation generated from linear regression. Validation of the sensitivity and specificity using a different set of data is needed in order to improve the generalizability of this finding. Second, the prevalence of uremic pruritus may be may be more prevalent in cold seasons . As this study was conducted in December, the prevalence of uremic pruritus may be relatively high. Third, the severity of pruritus may be under-estimated using the 5-D itch scale categories when compared to NRS categories (Table 3). As there is no gold standard measurement of pruritus available, we were not able to identify which measurements of pruritus was more reliable.
The 5-D itch scale is a reliable and multidimensional measure of uremic pruritus that is validated in hemodialysis patients. The 5-D itch scale categories are presented in this study based on its association with NRS categories. We purposed a transformation equation between the 5-D itch scale and NRS for pruritus measurements.
Numerical rating scale
This work is supported by grants from China Medical University under the Aim for Top University Plan of Taiwan`s Ministry of Education (A-3-2-A) and is partially supported by grants from Academia Sinica, Taiwan (grant number BI 10150264, BM102021124, BM103010089 and BM104010113).
Availability of data and materials
The data is available in Additional file 1.
JW contributed acquisition of data, HC performed the statistical analysis, CY drafted the manuscript, HR contributed acquisition of funding, TC contributed to the design and funding, MF revised the manuscript critically for important intellectual content, HH designed the study, CC supervised the study, FJ revised the manuscript critically for important intellectual content, JT, CT participated in the design of the study and final approval of the version to be published. All authors read and approved the final manuscript.
The results presented in this paper have not been published previously in whole or part. The authors have no conflicts of interest regarding this study. The grants from China Medical University had no role in the study design, collection of data, analysis, and interpretation of data.
Consent for publication
All authors read and approved the final manuscript.
Ethics approval and consent to participate
This study was approved by the institutional review board of China Medical University Hospital (CMUH 103-REC2-112) and a written informed consent was obtained from each patient.
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