| Sumario: | Objective: This study aimed to evaluate the diagnostic accuracy of SARC-F and SARC-CalF as screening tools for sarcopenia in patients with rheumatoid arthritis using the European Working Group on Sarcopenia in Older People 2 algorithm as the reference standard. Method: A cross-sectional study was conducted among 106 patients with rheumatoid arthritis diagnosed according to the 2010 ACR/EULAR criteria. Sarcopenia was assessed through handgrip strength, appendicular skeletal muscle mass (via bioelectrical impedance analysis), and gait speed, following the EWGSOP2 "Find – Assess – Confirm – Severity" (F-A-C-S) model. The diagnostic performance of SARC-F and SARC-CalF was evaluated using sensitivity, specificity, positive and negative predictive values (PPV, NPV), and receiver operating characteristic (ROC) curves. Results: Among the participants, 43.3% had probable sarcopenia (low muscle strength), 15% had confirmed sarcopenia (low muscle strength plus low muscle mass), and 11.3% had severe sarcopenia (low strength, low mass, and poor physical performance), according to EWGSOP2 criteria. SARC-F showed high sensitivity (86.2%) and NPV (91.3%) for probable sarcopenia but had low specificity (54.5%) and poor discrimination for confirmed (AUC: 0.43) and severe (AUC: 0.44) cases. In contrast, SARC-CalF demonstrated improved specificity (90.7%) and better AUC (0.63) for confirmed sarcopenia, although sensitivity remained low (32.3%). Both tools showed limited performance in detecting severe sarcopenia. Conclusion: SARC-F, with its high sensitivity, can serve as a first-line physiotherapy screening tool to identify patients with rheumatoid arthritis at risk of sarcopenia, enabling timely referral for muscle-strengthening interventions. SARC-CalF offers greater specificity for confirmed cases and supports individualized exercise planning. As neither tool alone detects severe sarcopenia, a two-step approach combining both questionnaires with confirmatory assessments is recommended to enhance early detection and optimize functional outcomes in physiotherapy practice.
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