Ethnic-specific cut-points for sarcopenia: evidence from black South African women

BACKGROUND/OBJECTIVES: Age-related muscle and fat mass (FM) changes are ethnicity specific. We aimed to develop a cut-point for the muscle mass component of sarcopenia for black South African (SA) women, and to assess its predictive value, in comparison to established cut-points, to identify functional ability among older black SA women. SUBJECTS/METHODS: In a cross-sectional study, a sarcopenia cut-point was calculated from dual energy X-ray absorptiometry (DXA)-derived appendicular skeletal muscle mass (ASM) indexes (ASMI) from two young black SA reference groups. The new cut-point was compared with the most recent Foundation for the National Institutes of Health (FNIH) criteria (ASM < 15.02 kg; and ASM(BMI) < 0.512), an internationally accepted cut-point (ASMI < 5.5 kg/m(2)) and a residual method adjusting for FM. All cut-points were then applied to 221 older black women to predict gait speed and handgrip strength. RESULTS: A cut-point of ASMI < 4.94 kg/m(2) was derived from the young SA reference groups. Using this cut-point, 9.1% of older women were classified as sarcopenic, compared with 16.7-38.7% using other cut-points. The only cut-points that significantly predicted low functional ability (low gait speed and low handgrip strength) in older black women were the new SA cut-point and the FNIH ASM criterion. Multivariate logistic regression models for both these cut-points significantly predicted low handgrip strength (odds ratio (OR) = 3.71, P = 0.007 and OR = 3.42, P = 0.001, respectively) and low gait speed (OR = 9.82, P = 0.004 and OR = 8.71, P = 0.008, respectively). CONCLUSIONS: The new SA cut-point had similar or greater odds of predicting reduced functional ability in older SA women when compared with other internationally accepted cut-points.