This was a single-centre, prospective observational study with a six month follow-up, conducted in a cohort of adult patients undergoing peritoneal dialysis (PD) between 2024 and 2025. Eligible participants were ≥18 years old and receiving maintenance PD at the time of enrolment. Patients with PD vintage<3 months at baseline were classified as incident PD patients, whereas those with PD vintage ≥3 months were considered prevalent PD patients. Sensitivity analyses were performed according to PD vintage. Exclusion criteria included: (i) hospitalization within the previous month, and (ii) PD prescribed for cardiorenal syndrome with an estimated glomerular filtration rate>20mL/min. A detailed patient flowchart and the completed STROBE checklist are provided as supplementary material (Supplementary Fig. 1, Supplementary Table 1).

Nutritional US was performed following the standardized protocol described by García-Almeida et al.9 All examinations were carried out using a digital color Doppler ultrasound system (SonoScape, China) equipped with a 6–12MHz linear probe, operating in B-mode.

QRF measurements were obtained on the dominant leg, at the distal third of the line connecting the anterior superior iliac spine and the superior border of the patella, with the patient in the supine position and the muscle fully relaxed. The transducer was placed perpendicular to the muscle surface. The following parameters were recorded: Y-axis thickness (mm), X-axis width (mm), cross-sectional area (cm2), and thigh supramuscular fat thickness (mm) (Fig. 1). Three consecutive measurements were obtained and averaged. Muscle parameters were normalized to height squared (m2) and body surface area (BSA) using the Du Bois formula.11

Fig. 1.

(A) Anatomical location of the ultrasound measurement point at the distal third of the imaginary line connecting the anterior superior iliac spine and the superior border of the patella. (B) Ultrasound image of the quadriceps rectus femoris (QRF), showing the X- and Y-axes and the traced cross-sectional area. (C) Location of the measurement point, midway between the xiphoid process and the umbilicus. (D) Ultrasound image showing the different layers of abdominal fat.

Abdominal adipose tissue was assessed at the midpoint between the xiphoid process and the umbilicus during relaxed expiration, with the peritoneal cavity drained. Superficial subcutaneous, deep subcutaneous, and preperitoneal fat layers were measured according to the standardized technique (Fig. 1). All nutritional ultrasound examinations were performed by a single trained operator to ensure methodological consistency.

Body composition was evaluated using multifrequency bioimpedance analysis (BCM®, Fresenius Medical Care, Germany) to obtain overhydration (OH), lean tissue index (LTI), fat tissue index (FTI), and phase angle at 50Hz.

Muscle strength was assessed using handgrip strength, measured with a handheld dynamometer (CAMRY EH101). Low muscle strength (dynapenia) was defined according to the EWGSOP2 criteria (handgrip<27kg in men and <16kg in women).12 Physical performance was evaluated using the Short Physical Performance Battery (SPPB).13

Nutritional status was assessed using the Malnutrition–Inflammation Score (MIS).14 Laboratory parameters included serum creatinine, phosphorus, dialysis adequacy (weekly Kt/V), and residual kidney function (RKF), normalized protein catabolic rate (nPCR), C-reactive protein (CRP), albumin, prealbumin, and lipid profile.

PEW was classified according to the simplified 2014 International Society of Renal Nutrition and Metabolism (ISRNM) score,15 using the following variables: serum albumin ≤3.8g/dL, body mass index (BMI) ≤23kg/m2, serum creatinine normalized by body surface area (sCr/BSA) ≤3.8mg/dL/m2, and protein intake ≤0.8g/kg/day. Protein intake was estimated using normalized protein catabolic rate (nPCR), which was used as a surrogate marker of dietary protein intake.16 Moderate PEW was defined by the presence of two criteria, and severe PEW by three or more criteria. Nutritional US, functional assessments, and biochemical measurements were performed on the same day to minimize variability.

Continuous variables are presented as mean (standard deviation, SD) or median (interquartile range, IQR), according to their distribution. Categorical variables are expressed as frequencies and percentages. Between-group comparisons were performed using the Student's t-test or Mann–Whitney U test for continuous and independent variables or paired-Student's t/Wilcoxon test for paired samples, and χ2 test/McNemar test for categorical variables, as appropriate.

Associations between nutritional ultrasound parameters and body composition, functional, and nutritional markers were evaluated using Pearson correlation coefficients. The ability of ultrasound-derived parameters to discriminate PEW and dynapenia was assessed using receiver operating characteristic (ROC) curve analysis, with calculation of the area under the curve (AUC) and 95% confidence intervals (CI). Given the limited sample size, multivariable analyses were restricted to exploratory models adjusted for clinically relevant covariates (age, sex, BMI and PD vintage) to minimize overfitting. Additionally, given that missing data were likely not missing at random, with a probable higher proportion of patients lost to follow-up due to kidney transplantation, a complete-case analysis including only patients with at least 6 months of follow-up was performed. Separate multivariable linear regression models were constructed to assess the association between QRF Y-axis thickness and body composition variables (LTI and phase angle), with each model adjusted for these covariates.

Statistical significance was set at p<0.05. Analyses were performed using Stata version 16 (StataCorp LLC, College Station, TX, USA).

The study was approved by the Ethics Committee (approval number PI 75/24). All procedures were conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. Written informed consent was obtained from all participants prior to enrolment.

A total of 59 patients undergoing PD were included in the baseline analysis. Mean age was 64.2±14.0 years, and 61.0% were male. The majority of patients were receiving automated peritoneal dialysis (69.5%), and 32% were using icodextrin. Median PD vintage was 0.9 months (IQR 0.4–15.5). At baseline, 37 patients (62.7%) were classified as incident PD patients (<3 months on PD), whereas 22 patients (37.3%) were classified as prevalent PD patients (≥3 months on PD).

Comorbid conditions included hypertension (86.4%), diabetes mellitus (33.9%), and ischemic heart disease (20.3%). The most frequent causes of kidney failure were glomerular disease (32.7%) and diabetic kidney disease (18.0%). Mean weekly Kt/V was 2.4±0.6, residual kidney function was 5.5±3.0mL/min/1.73m2, and two thirds of patients achieved SPPB scores ≥10, indicating preserved physical performance. Baseline demographic, clinical, biochemical, and body composition characteristics are summarized in Table 1.

Mean QRF Y-axis thickness was 11.1±3.0mm, and mean cross-sectional area was 3.5±1.4cm2. Women exhibited significantly greater thigh and abdominal adipose tissue thickness than men, except for preperitoneal fat, whereas men showed higher QRF cross-sectional area and X-axis width.

QRF Y-axis thickness showed moderate positive correlations with lean tissue index (LTI), phase angle, handgrip strength, and SPPB score, and inverse correlations with the Malnutrition–Inflammation Score (MIS) and PEW severity. QRF X-axis width and cross-sectional area were also positively associated with handgrip strength and LTI. In contrast, superficial thigh fat and abdominal fat compartments correlated positively with fat tissue index (FTI) and body mass index, while abdominal fat thickness showed an inverse association with MIS (Table 2). In exploratory adjusted analyses, QRF Y-axis thickness remained associated with LTI after adjustment for age, sex and BMI (β=0.38; 95% CI 0.14–0.62; p=0.002). Similarly, QRF Y-axis thickness remained associated with phase angle after adjustment for the same covariates (β=1.40; 95% CI 0.65–2.16; p<0.001).

At baseline, 44.1% of patients met criteria for moderate PEW and 15.3% for severe PEW. Low handgrip strength (dynapenia) was present in 22.0% of the cohort and was more frequent among men.

Patients with severe PEW had lower muscle thickness (Y-axis: 7.93mm, SD 1.82) compared with those with moderate PEW (11.51mm, SD 3.30) and those without PEW (11.95mm, SD 2.31); after adjustment for age and sex using analysis of covariance (ANCOVA), significant differences in QRF Y-axis thickness across PEW categories remained significant (p=0.009).

They also showed a trend toward lower handgrip strength: severe PEW, 22 (SD 6.06) vs moderate PEW, 27.62 (SD 9.01) vs no PEW, 29.54 (SD 7.67), p=0.067. In addition, the severe PEW group had lower functional capacity as measured by the SPPB: severe PEW 7.1 (SD 5.0) moderate PEW 10.0 (SD 2.7) and no PEW 10.12 (SD 2.4) p=0.03 and a trend toward a lower phase angle: severe PEW, 3.96 (SD 0.8) vs moderate PEW, 4.72 (SD 0.9) vs no PEW, 4.87 (SD 1.0), p=0.05. However, we did not observe differences in LTI.

ROC analysis demonstrated that QRF Y-axis thickness discriminated PEW with an area under the curve (AUC) of 0.68 (95% CI 0.54–0.81; p=0.012). Reduced preperitoneal fat thickness also showed discriminatory capacity for PEW (AUC approximately 0.66, 95% CI 0.51–0.80; p=0.03). In addition, QRF Y-axis thickness identified dynapenia with an AUC of 0.72 (95%CI 0.58–0.86; p=0.002). More results in Supplementary Table 2.

Women were younger than men but did not differ significantly in comorbidity burden, PD prescription, dialysis adequacy, or residual kidney function. They exhibited a lower prevalence of dynapenia and a lower degree of overhydration.

Nutritional US showed that women had smaller QRF dimensions, particularly X-axis width and cross-sectional area, diminishing when normalized by height squared and BSA. In contrast, women demonstrated greater thigh supramuscular fat and increased abdominal adipose tissue across superficial and deep layers, except preperitoneal fat. These findings were consistent with bioimpedance results, where women showed higher fat tissue index (FTI) and lower lean tissue index (LTI) (Table 1).

Of the 59 patients enrolled at baseline, 45 completed the six-month follow-up. Attrition was mainly due to kidney transplantation (n=10), transfer to in-centre haemodialysis (n=3), or transition to home haemodialysis (n=1). Among the patients who did not complete follow-up compared with completers, non-completers had higher baseline QRF Y-axis thickness, LTI and phase angle (p<0.05), suggesting a better baseline morphofunctional profile. Baseline age, BMI, albumin, residual kidney function, diabetes, PEW category, PD vintage and PD modality were broadly similar between groups. Baseline characteristics according to completion of follow-up are shown in Supplementary Table 3.

Over six months, handgrip strength, SPPB score, MIS, LTI, and phase angle remained stable at the group level. No significant changes in overall PEW prevalence were observed.

In contrast, nutritional US detected a significant increase in QRF Y-axis thickness (10.7±2.9mm to 11.9±3.3mm; p=0.003) (Fig. 2) and QRF cross-sectional area (p=0.032), even when adjusted by height squared or BSA, while X-axis width remained unchanged. The change in QRF Y-axis thickness and cross-sectional area did not differ between incident and prevalent PD patients. Incident patients showed a mean increase in QRF Y-axis thickness of 1.09mm, while prevalent patients showed a comparable change, with no significant between-group difference (Difference=−0.12mm; 95% CI −1.57 to 1.34; p=0.874). Despite adjusting for age, sex, and BMI, no significant differences were observed. FTI and thigh supramuscular fat thickness increased during follow-up, whereas abdominal fat compartments remained stable. The change in thigh supramuscular fat differed between incident and prevalent PD patients. Incident patients showed a greater increase in thigh supramuscular fat than prevalent patients (median change +1.28mm [IQR 0.25 to 2.00] vs −0.11mm [IQR −1.44 to 0.87], respectively; p=0.05). No significant differences were observed between incident and prevalent PD patients in the 6-month changes in total abdominal fat. Laboratory parameters showed no clinically relevant changes, except for a small decrease in serum albumin (Table 3).

Fig. 2.

Longitudinal changes over 6 months assessed by nutritional ultrasound, bioimpedance analysis, and functional markers. Nutritional ultrasound showed a significant increase in muscle thickness and greater fat accumulation, including thigh supramuscular fat, whereas abdominal fat remained unchanged. Functional markers remained stable. Abbreviations: NUS, nutritional ultrasound; QRF, quadriceps rectus femoris.