The Significance of Body Mass Index in Calculating the Cut-Off Points for Low Muscle Mass in the Elderly: Methodological Issues

OBJECTIVES Cut-off points (COPs) for appendicular lean mass (ALM) index, essential to define low muscle mass (LMM) in the elderly, have never been officially defined for Poland. The aim of the study was to establish them. Additionally, the significance of body mass index (BMI) for correctly defining the COPs in a young, healthy reference group was assessed. METHODS The study was composed of reference group (n = 1113) and the elderly group (n = 200). In all subjects, body composition was assessed by bioimpedance analysis, and ALM index was calculated. Next, COPs (kg/m(2)) were set up for the whole reference group and for particular subgroups with different BMIs separately. They were used to diagnose sarcopenia in the elderly. RESULTS COP for all young females was 5.37 (COP-F), while it was equal to 5.52 (COP-F2) when only those with a recommended BMI (18.50-24.99 kg/m(2)) were taken into consideration. For males, it was 7.32 and 7.29, respectively. Only 7% of elderly females had LMM based on COP-F and 15% had LMM based on COP-F2 (P < 0.05); for males, the percentages were 18% and 16%, respectively. CONCLUSIONS COPs for LMM for Poland are 5.52 kg/m(2) (females) and 7.29 kg/m(2) (males). The reference group BMI is an important factor in establishing COPs for low muscle mass.