Arm circumference as a marker of muscle mass: cutoff values from NHANES 1999-2006.

Although mid-upper arm circumference (MUAC) is a potential marker of skeletal muscle (SM), no study has proposed MUAC cutoff points using a large young reference population. Additionally, growing evidence highlights the impact of excess adiposity on anthropometric markers, which can mask their value in evaluating SM. This study aimed to propose cutoff points for MUAC as a marker of muscle mass, along with BMI-adjustment factors for individuals outside the normal BMI range (18.5-24.9 kg/m2), using data from the NHANES 1999-2006 sample. Anthropometric and appendicular lean soft tissue (ALST by DXA) data from the adult NHANES sample (age ≥18 years) were divided into sex (males: M; females: F), age, ethnicity, and self-reported race subgroups. Adults aged 18-39 years with a BMI of 18.5-24.9 kg/m2 were used as the reference population, and MUAC cutoff points were derived at 1 and 2 standard deviations below the mean. Pearson's correlation (r) was used to assess the correlation between MUAC and ALST. Survey-weighted linear regression analysis was used to derive BMI-adjustment factors for MUAC. A total of 18,195 individuals were included (weighted proportion: 49.4% M, mean age 43.9 years, 95% CI 43.4 to 44.4). MUAC showed a strong positive correlation with ALST index (ALST/height2) (r = 0.83 for males, r = 0.79 for females). Rounded cutoff points for low MUAC were 28 cm (M) and 25 cm (F), and for very low MUAC, 26 cm (M) and 23 cm (F). Overall BMI-adjustment factors were: -3 cm(M), -2cm(F) (BMI: 25-29.9); -7cm(M), -6 cm(F) (BMI: 30-39.9); -10cm(M), -9cm(F) (BMI: >40). This study proposes practical MUAC cutoff points, a potential marker of SM, along with BMI adjustment factors for individuals with excess weight, aiming to reduce errors in using MUAC for this purpose. Our results have the potential to enhance clinical routine assessments.