Children’s weights correlate more strongly with mid-arm circumference (MAC) than with age, height or foot-length

Abstract

Background: Rapid and accurate estimation of a child's weight is often necessary when time is limited, to provide appropriate drug and fluid doses. Commonly used methods of weight estimation use height- or age-based calculations. It is not known which method is most accurate in Chinese children. Objective: To determine which of the following parameters most strongly correlates with weight: age, height, foot-length, or mid-arm circumference (MAC), and to derive new weight estimation formulae. Design: Population-based observational study. Ethical approval was obtained from the Chinese University of Hong Kong. Participants: 1368 Chinese children (752 boys, 616 girls), 1–11.9 years old, in schools and kindergartens in Hong Kong. Interventions: Height, foot-length, and MAC were measured to 0.1 cm, weight to 0.2 kg. Main outcome measures: Correlation coefficients (r) for weight with each parameter. Subgroups were analyzed according to the age groups in Advanced Trauma Life Support: toddler (1–2.9 years), preschool (3–5.9 years), school-age (6–11.9 years). Linear regression was used to derive formulae for weight estimation. Bland-Altman plots were used to assess the precision of age-based, height-based, and MAC-based weight estimations. Results (Table 1, Figure 1): Overall, and in pre-school and school-age children, weight was correlated more strongly with MAC than with any of the other parameters. In toddlers, weight did not correlate with any parameter significantly more strongly than with any other. Age was related to weight according to the formula: Weight in kg = (Age × 3) + 5. MAC was related according to the formula: Weight = (MAC − 10) × 3. Although Broselow was superior to MAC-based estimation in younger children, there was no difference in bias or precision in school-age children. Conclusion: Weight correlates with MAC more strongly than with age, height, or foot-length. Estimates of children's weight could be based on mid-arm circumference: W = (MAC − 10) × 3. We propose using a purpose-made arm tape that could be used in conjunction with the Broselow color-coded system. This would be especially useful for older children.