Assessment of Sarcopenia Using Rectus Femoris Ultrasound in Emergency Patients—A Cross-Sectional Study

Background: Sarcopenia is a progressive muscle disorder commonly associated with aging and chronic diseases. It has been linked to worse clinical outcomes and increased vulnerability during acute illness. However, its prevalence in emergency department (ED) populations remains underexplored. This study aimed to evaluate the presence of sarcopenia among ED patients using ultrasound, determine its relationship with underlying comorbidities, and assess its association with in-hospital complications. Methods: We conducted a prospective, observational, cross-sectional study at the Infanta Cristina University Hospital (Madrid, Spain) from January to May 2024. A total of 150 patients aged 18 years and older who presented to the ED were assessed for sarcopenia using rectus femoris ultrasound. Sociodemographic, clinical, and laboratory variables were collected. A multivariate logistic regression model was used to identify independent predictors of in-hospital complications. Patients were followed for 30 days to evaluate outcomes. Comparisons were made between diagnostic groups and sarcopenia indices. Results: The mean age of the cohort was 70.7 years (SD 18.15), and 52% were male. Neurological diseases were associated with the highest degree of sarcopenia (mean Y-axis: 0.93 cm), followed by digestive (1.05 cm), hematological (1.05 cm), and cardiovascular diseases (1.08 cm). Patients who developed in-hospital complications had lower mean muscle thickness values compared to those without complications (1.08 cm vs. 1.24 cm; p < 0.05). Sarcopenia was significantly correlated with the presence of comorbidities and poor clinical outcomes. Conclusions: These findings support the integration of sarcopenia screening protocols into emergency care and highlight the need for studies exploring early nutritional or rehabilitation interventions targeted at high-risk patients.