Discriminative Ability and Associations of Sarcopenia Using Point-of-Care Ultrasound with Functional, Mobility and Frailty Status in Older Inpatients.

Background/Objectives: We aimed to assess the discriminative ability of point-of-care ultrasound (POCUS) of the rectus femoris (RF) to detect sarcopenia and to examine associations of these sarcopenia measures with functional, mobility, and frailty status among older inpatients. Methods: Data were analysed from 161 patients aged 70 years and older consecutively admitted to a tertiary geriatric rehabilitation hospital between October and December 2023. The RF thickness and cross-sectional area (CSA) were measured using POCUS applying validated cut-offs. Ability of muscle ultrasound to detect sarcopenia based on bioelectrical impedance analysis (BIA) as the reference standard was calculated using receiver operating characteristics analyses (ROC). Second, associations of sarcopenia measures based on either the ultrasonographic RF thickness, or the RF cross-sectional area with functional, frailty, and mobility status were analysed using multivariable logistic regression analyses. Results: Mean age was 84.0 years (standard deviation (SD) 6.1 years) and 64.4% were women. Overall, 31 (19.3%) patients had sarcopenia based on low grip strength and low muscle mass using the BIA. The mean ultrasonographic RF thickness and CSA were 13 mm (SD 4.1) and 4.3 cm2 (SD 1.7), respectively. Correlation coefficients of the RF thickness with BIA-muscle mass were r = 0.52 in males, versus r = 0.40 in females. Both sarcopenia measures using the RF thickness and CSA were positively associated with functional (adjusted odds ratio (OR) 9.3 (95% CI 3.7-23.4) and 9.2 (3.6-23.7)) and frailty status (OR 4.0 (95% CI 2.1-12.1) and 4.3 (1.8-10.4)). None of the sarcopenia measures were significantly associated with mobility status. Conclusions: Rectus femoris thickness and CSA measured by POCUS showed a fair discriminative ability to detect sarcopenia based on BIA, suggesting that BIA and POCUS measure different aspects of muscle health. A strong association between sarcopenia based on POCUS and functional and frailty status suggest the potential utility of POCUS in the diagnostic evaluation of sarcopenia among older hospitalised patients; however, further study is required. Research should focus on establishing valid sex-specific cut-offs for grip strength and muscle mass, with the ultimate goal of developing a low-cost, bedside, and sensitive diagnostic toolkit for detecting sarcopenia in older patients.