Rationale: The use of muscle ultrasound (US) is a trending method in clinical practice. It's reliable and valid for the assessment of muscle size in older adults. 1 The aim of the study is to define muscle US cut-off values for the evaluation of sarcopenia in older outpatients. Methods: A total of 400 patients (65 years) applied to geriatric outpatient clinic were assessed and 312 of them (64.5%, female) were involved. Comprehensive geriatric assessment (including frailty status), anthropometric measurements and handgrip strength (HGS) were evaluated. Rectus femoris muscle cross-sectional area (RF-CSA) was measured and cut-off values that predict low muscle strength were determined. Results:The median age was 72 (min-max, 65-93), 64.5 % were female, and 43.8 % (n¼ 137) had low HGS. 25.2% and 23.3% of patients were prefrail and frail, respectively according to Clinical Frailty Scale. RF-CSA had a good correlation with HGS (r:0.578, p<0.001). Cut-off values to predict low HGS for RF-CSA, body mass index (BMI) adjusted RF-CSA and height square adjusted RF-CSA are given in Table-1. Abbreviation: RF-CSA, rectus femoris cross-sectional area; BMI, body mass index (kg/m 2 ); AUC, area under curve; PPV, positive predictive value; NPV, negative predictive value Conclusion: The cut-off values for muscle US for the assessment of muscle mass as a part of the sarcopenia evaluation in clinical practice to guide for future studies are defined. References: