Equation-dependent anthropometric muscle-mass estimates and functional screening limitations in home-bound older...

Home health care (HHC) patients are typically older, multimorbid and functionally dependent, limiting direct body-composition assessment. Anthropometric equations offer practical appendicular lean soft tissue (ALST) estimates but may classify patients differently. The primary aim was to quantify equation-dependent variation in low-muscle-mass classification across five dual-energy X-ray absorptiometry (DXA)-referenced anthropometric ALST equations. Secondary aims were to assess agreement, discrimination by the Strength, Assistance with walking, Rise from a chair, Climb stairs and Falls (SARC-F) questionnaire, structural coupling in calf-circumference discrimination, and adiposity-related classification differences.

This retrospective cross-sectional study included 392 HHC patients followed at a tertiary referral centre (September 2024-September 2025). Five DXA-referenced equations (Gomes, Kawakami, Santos, Sun and Xu Wen) were applied. Agreement was assessed by Bland-Altman analysis and Cohen kappa. Discrimination was quantified by the area under the receiver operating characteristic curve (AUC) with 95% confidence intervals (CIs). Calf-circumference AUCs were compared according to whether calf circumference was present in the outcome-defining equation. Body mass index (BMI)-adjusted calf circumference and mid-upper arm circumference (MUAC) were sensitivity analyses.

Low-muscle-mass prevalence ranged from 0.0% (Sun) to 50.3% (Santos); Kawakami, Xu Wen and Gomes yielded 26.5%, 14.0% and 13.0%. Bland-Altman bias ranged from -1.18 to +4.33 kg/m², with kappa 0.435-0.492 (Sun 0.000). SARC-F did not discriminate Kawakami-defined low muscle mass: AUC 0.563 (95% CI 0.480-0.646) in women and 0.467 (95% CI 0.362-0.571) in men. Calf-circumference discrimination was higher for equations containing calf circumference than for circumference-free equations. In obese patients, Kawakami height-squared ALST index classified 1.5% as low versus 86.3% with BMI-adjusted calf circumference and 71.0% with BMI-adjusted MUAC.

Anthropometric low-muscle-mass classification in home-bound older adults is strongly equation-dependent. SARC-F showed poor discrimination, while calf-circumference discrimination was influenced by structural coupling. Height-squared indices may under-detect low muscle mass in obesity relative to BMI-adjusted circumference markers. Without direct body-composition and muscle-strength measurements, these findings do not establish sarcopenic obesity.