ABSTRACT Purpose The main objective of the Sarco‐Detect study was to evaluate diagnostic tools—bioelectrical impedance analysis (BIA) and handgrip strength (HGS)—for determining sarcopenia compared with computed tomography (CT). The secondary aim was to evaluate the SARC‐F questionnaire as a screening tool and to investigate the impact of muscle loss on quality of life, fatigue, HGS, and the association between previous physical activity and muscle loss. Methods The study was conducted at the University Cancer Center Schleswig‐Holstein. To assess muscle mass status, BIA and HGS were measured in patients with cancer and compared with CT. Additionally, EORTC QLQ‐C30, FACIT‐Fatigue Scale, BSA, and SARC‐F questionnaires were administered. Results One hundred thirty one patients were recruited. Fourteen patients showed a CT‐SMI below the reference values by Van der Werf et al. (2018). Thirteen patients showed reduced HGS. CT‐SMI and HGS correlated significantly ( r = 0.492, p = 0.001). The phase angle of the BIA correlated significantly with CT‐SMI ( r = 0.441, p = 0.001) and HGS ( r = 0.493, p = 0.001). Patients with reduced HGS presented significantly higher appetite loss compared with patients with preserved HGS. Patients with preserved HGS showed a higher quality of life than patients with reduced HGS. FACIT‐Fatigue scores differed significantly between patients with reduced HGS and those with preserved HGS ( F (1, 104) = 3.991, p = 0.048; U = 321.000, Z = −2.088, p = 0.037). Activity index correlated moderately with fatigue symptoms and quality of life. The SARC‐F showed a sensitivity of 18.8% and specificity of 96.6% for HGS, and a sensitivity of 31.3% and specificity of 90.7% for CT‐SMI. Conclusions CT‐SMI and HGS correlated positively and significantly. The BIA phase angle correlated with CT‐SMI and HGS. Reduced HGS is associated with increased appetite loss, higher fatigue, and lower quality of life. SARC‐F questionnaire appears suitable for identifying patients without sarcopenia. Trial Registration German Clinical Trials Register: DRKS00035258
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