Study population and design
This cross-sectional study included clinically stable Japanese outpatients in multicenter hemodialysis unit from April 2012 to April 2018. Exclusion criteria included age <18 years, dialysis vintage <6 months, and refusal to participate. This study was approved by the Ethical Committee of International University of Health and Welfare (Approval number. 17-Io–95).
Demographic and clinical laboratory findings
Patients’ demographics, such as age, dialysis vintage, and body mass index (BMI) were investigated. Laboratory values of serum albumin, serum hemoglobin, C reactive protein, serum intact parathyroid hormone, standardized dialysis volume (Kt/V), and normalized protein catabolic rate (nPCR) were also collected.
Assessment of nutritional status and classification of malnutrition by GNRI and P
GNRI was calculated using the formula described elsewhere: GNRI = [1.489×serum albumin (g/L)] + [41.7×(body weight/ideal body weight)].5,9 Ideal body weight was defined as weight with a BMI value of 22 kg/m2.10 Malnutrition was defined as a GNRI <90 according to previous studies.3,11
P was classified into three categories according to the guidelines of the Japanese Society of Dialysis Therapy12: a P of 3.5–6.0 mg/dL was considered the reference range, P <3.5 mg/dL was considered decreased, and P >6.0 mg/dL was considered abnormally high.12
In addition, GNRI and P were categorized together as follows: the reference category was set as GNRI ≥90 and 3.5≤ P ≤6.0, whereas six other categories, including 2 GNRI categories and 3 P categories were also formed.
Measurement of indicators related to sarcopenia
The diagnosis and definition of sarcopenia have been revised in 2018.13 In its 2018 definition, low muscle strength was pointed out as the primary parameter of sarcopenia; presently, muscle strength is considered the most reliable measure of muscle function.13 In addition, physical performance was formerly considered part of the core definition of sarcopenia.13 In the definition of 2018, physical performance was regarded as an index for determining severity. According to this new algorithm,13 we evaluated muscle strength by using grip strength test and physical performance by using Short Physical Performance Battery (SPPB) to determine probable sarcopenia. The cut-off value of grip strength was 26 kg for men and 18 kg for women from an Asian consensus14 and that of SPPB was 8 points. Grip strength was measured using a Smedley-spring type dynamometer (101A HATS, Tokyo).
All values are expressed as mean ± standard deviation (SD) or percentage, whenever appropriate. Descriptive statistics of nutrition and sarcopenia index were calculated by age group and were compared by one-way analysis of variance (ANOVA) and post hoc multiple comparisons. To analyze the relationship between probable sarcopenia and nutritional disorder, multiple logistic regression analyses were performed with grip strength and SPPB as dependent variables, and GNRI only, P only, and 6 categories of combined GNRI and P as independent variables. Results from logistic regression analyses were presented as odds ratios (OR) with 95% confidence intervals. A P value < 0.05 was considered statistically significant. Statistical analyses were performed using SPSS (version 24, IBM, Tokyo).