Diagnostic Accuracy of Rectus Femoris Ultrasound for Identifying Sarcopenia as Defined by the European Working Group on Sarcopenia in Older People 2 in Haemodialysis Patients

Background/Objectives: Sarcopenia is highly prevalent in patients with end-stage renal disease and is associated with adverse outcomes. We evaluated the diagnostic accuracy of rectus femoris ultrasound, compared with bioimpedance spectroscopy (BIS), for identifying sarcopenia defined by the European Working Group on Sarcopenia in Older People 2 (EWGSOP2) in haemodialysis patients, and derived overall and sex-specific ultrasound cut-off values. Methods: In this single-centre cross-sectional study, haemodialysis patients were assessed for sarcopenia according to EWGSOP2 criteria. Rectus femoris thickness (RFT) and cross-sectional area (CSA) were measured by ultrasound, while BIS was used to estimate body composition. Receiver operating characteristic (ROC) curves were constructed, and areas under the curve (AUC) with 95% confidence intervals were estimated to assess the ability of ultrasound and BIS-derived parameters to discriminate confirmed sarcopenia. Optimal overall and sex-specific cut-off values were determined using the Youden index. Results: A total of 115 patients were included. Median age was 73.0 years [IQR: 63.0–82.0], 67.0% were men. Sarcopenia was diagnosed in 50 patients (43.5%; 95%CI: 34.3–53.0). RFT and CSA showed moderate diagnostic accuracy for confirmed sarcopenia, with AUCs of 0.73 (95%CI: 0.63–0.82) and 0.72 (95%CI: 0.63–0.81), respectively. Ultrasound cut-offs of 11.9 mm for RFT and 4.4 cm2 for CSA yielded high sensitivity and moderate specificity. Conclusions: Rectus femoris ultrasound represents a feasible bedside approach for identifying EWGSOP2-defined sarcopenia in haemodialysis patients. Its diagnostic performance was comparable to that of BIS-derived measures, supporting its potential use in routine clinical practice. Further studies are warranted to validate the proposed cut-off values.