Validation and applicability of appendicular skeletal muscle mass estimation equations in a geriatric hospital setting.

BACKGROUND&AIMS: Sarcopenia and malnutrition are linked to adverse outcomes in older adults, requiring muscle mass assessment for diagnosis. While specialized equipment is recommended, limited accessibility highlights the need for alternative methods. Various skeletal muscle mass estimation equations exist, but their validity across clinical settings is uncertain. This study evaluated the validity and applicability of previously reported appendicular skeletal mass (ASM) estimation equations in older adults across two hospital settings.

METHODS

This study utilized registry data from the National Center for Geriatrics and Gerontology, including patients aged ≥65 years from a frailty outpatient clinic and geriatric ward. ASM was assessed using dual-energy X-ray absorptiometry (DXA) as the reference standard. A comprehensive review identified multiple ASM estimation equations based on age, sex, height, weight, and creatinine-to-cystatin C ratio (Cre/CysC). As an exception, one skeletal muscle mass index (SMI) estimation equation was included in the analysis. In both groups, intraclass correlation coefficients (ICCs) were calculated to assess the agreement between ASM estimates and DXA measurements. Estimation errors were standardized as T-scores, plotted, and visualized with 95 % confidence ellipses for each group.

RESULTS

The analysis included 856 patients from the frailty clinic group (mean age: 78.2 ± 6.1 years, 58.3 % women) and 328 from the geriatric ward group (mean age: 86.2 ± 6.4 years, 60.7 % women). ICCs between the ASM estimation equations and DXA were generally higher in the frailty clinic group. Several equations achieved ICC ≥0.9 in the frailty clinic group and ICC ≥0.8 in the geriatric ward group. Equations based on age, sex, height, and weight performed well in both groups, with minimal benefit from adding Cre/CysC. Estimation errors showed no substantial differences between groups.

CONCLUSION

Several ASM estimation equations showed strong agreement with DXA in older adults across outpatient and inpatient settings. While dedicated equipment is ideal, using common patient data for muscle mass estimation improves accessibility and may support the wider adoption of muscle assessment for sarcopenia and malnutrition diagnosis.