The application of different appendicular skeletal muscle cutoff points and research definitions associated with health-related quality of life in Korean older people: data from KNHANES 2008–2011

BACKGROUND This study was conducted to determine the prevalence of a low appendicular skeletal muscle index (ASMI) using three cut-off points (mean ASMI-2SD of a gender-specific young reference group (aged 18-39 years), mean ASMI-1SD of a gender-specific young reference group, and the lower 20 percentile value of a gender-specific older group (aged ≥ 65 years)) in Korean older people and the relationship between ASMI and subjective health-related quality of life. METHODS This study utilized data acquired during the Korean National Health and Nutrition Examination Survey (KNHANES) from 2008-2011. Dual-energy X-ray absorptiometry body compositional data was obtained from a subsample of 6538 subjects (men 2804, women 3734) aged 18-39 and 4413 subjects (men 1872, women 2541) aged 65 years and older. The three definitions of low appendicular skeletal muscle and the EQ-5D-3 L-Korean descriptive system were applied to Korean older people. RESULTS For the ASMI cutoff points used, in men, the three cutoff points were ASMI 2SD (6.09 kg/m2), ASMI 20 (6.48 kg/m2), and ASMI 1SD (6.95 kg/m2). In women, ASMI 2SD (4.38 kg/m2) was the lowest, followed by ASMI 1SD (4.96 kg/m2) and ASMI 20 (5.33 kg/m2). Proportions of older subjects with a low ASMI using the three cutoff points were 9.7% (ASMI 2SD) and 40.9% (ASMI 1SD) in men, and 0.7% (ASMI 2SD) and 7.4% (ASMI 1SD) in women. By multivariate ordinal logistic regression analysis, men with a low ASMI had significantly high odd ratios for the three domains of mobility (p < 0.001), self-care (p = 0.005), and usual activities (p = 0.004) among the five domains of the EQ-5D and EQ-5D index (p = 0.010). CONCLUSIONS The ASMI 2SD cut-off points for older Koreans, 6.09 kg/m2 for men and 4.38 kg/m2 for women, resulted in low prevalences of a low ASM, that is, 9.7% for men and 0.7% for women, and showed low clinical usefulness due to very low determined prevalence in women. Hence, we suggest that the cut-off point of the lowest 20% of Korean older people (men: 6.48 kg/m2, women; 5.33 kg/m2) be used for older Koreans.