Mid-arm circumference can be used to estimate weight of adult and adolescent patients.

OBJECTIVES: Many drug and fluid regimens in emergency medicine are weight dependent in adults, but no standard adult weight estimation tools exist. Paediatric weight is often estimated in emergency situations using methods based on age or height when direct measurement is not possible, and recently, methods based on mid-arm circumference (MAC) have also been developed. The aim of this study was to derive and validate an accurate MAC-based method for weight estimation for use in all age groups.

METHODS: Data were obtained from the US National Health and Nutrition Examination Survey (NHANES). MAC-based methods of weight estimation were derived in 8498 subjects (5595 adults aged 16-80 years, 2903 children aged 1-15.9 years) from the NHANES 2011-2012 dataset, using linear regression. NHANES 2009-2010 was used for validation in 9022 subjects (6049 adults aged 16-79 years, 2973 children aged 1-15.9 years).

RESULTS: A simplified method of MAC-based weight estimation was derived from linear regression equation: weight in kg=4×MAC (in cm)-50. On validation, results in children aged 1-10.9 years were poor. In adults and children aged 11-15.9 years, over 60%, 90% and 98% of estimates fell, respectively, within 10%, 20% and 30% of actual weights when using the simplified formula.

CONCLUSIONS: In this description of a method for estimating weight in adults, we have derived and validated a simplified formula that is at least as precise in adults and adolescents as commonly used paediatric weight estimation tools in children.