Body mass index is not suitable for assessing body composition in children with spastic cerebral palsy

Purpose: To measure body composition by using bioelectrical impedance analysis (BIA) and body mass index (BMI) and to investigate the correlation and agreement between BMI and fat mass percentage in children with spastic Cerebral Palsy. Materials and methods: BIA was used to assess fat mass percentage and BMI was determined from body weight and height. BMI and fat mass percentage were both categorized into five categories. The association between fat mass percentage and BMI was assessed using Pearson’s correlation coefficient. Agreement between BMI and fat mass percentage was investigated with weighted Cohen’s kappa coefficient. Results: One hundred and three children with CP across all Gross Motor Function Classification Levels (61% boys, mean age 9 years) were included. Mean BMI was 18.3 kg/m² and mean fat mass was 24.9%. A large inter-subject variability was found with a weak correlation between BMI and fat mass percentage in children with a BMI < 20 kg/m². Little agreement (k = 0.299, CI 0.16–0.44) between the categorization of children based on BMI and based on fat mass percentage was found. Interpretation: The large inter-subject variability in fat mass percentage combined with little agreement between the BMI and BIA categories suggests that BMI is not a suitable measure of fat mass in children with CP.IMPLICATIONS FOR REHABILITATION Using body mass index (BMI) and instead of fat mass percentage increases the risk of misclassifying body composition in children with spastic Cerebral Palsy. Children with a BMI < 20 kg/m² are more at risk to be misclassified for body composition.