The Validity of Ultrasonographic Measurements of the Rectus Femoris Muscle in Older Adults with Sarcopenia in Thai Population

Purpose: This study aimed to determine the validity of ultrasonographic measurement of the rectus femoris muscle (RFM) thickness as a screening tool for low appendicular muscle mass (ASM) to diagnose sarcopenia and to determine the cut-off point of RFM thickness in the Thai population.Patients and methods: We enrolled 857 community-dwelling adults aged 60 years and older who were diagnosed with sarcopenia using the Asian Working Group for Sarcopenia-2019 algorithm. The RFM thickness was measured using ultrasonography and compared with bioelectrical impedance analysis (BIA) data. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were evaluated, and the area under the receiver operating curve (AUROC) was used to determine the accuracy of the test.Results: A total of 857 participants were included in the study. Overall, when the cut-off values of RFM thickness of <1.1 cm were used for male and <1 cm for female, the highest sensitivity for sarcopenia diagnosis was 90.9% and specificity was 92.2%. The PPV was 76.6, and the NPV was the highest at 97.3. The highest sensitivity for the diagnosis of severe sarcopenia was 92.5% and specificity was 97.4%. The AUROC of the cut-off point of RFM thickness for the diagnosis of sarcopenia was 0.92 (95% confidence interval [CI], 0.89-0.94); for severe sarcopenia, it was 0.95 (95% CI, 0.92-0.98).Conclusion: Measuring RFM thickness using ultrasonography is a feasible and reliable screening test for sarcopenia, and the cut-off values of <1.1 cm for male and <1 cm for female showed the highest accuracy for confirming low ASM in the Thai population.