During a routine consultation, the recommended assessment tools for evaluating obesity in children include measuring and recording the child's height and weight to calculate their BMI, which should then be classified using age- and sex-specific BMI centile charts. Specifically, overweight is classified as BMI at or above the 91st centile (+1.34 SD), clinical obesity at or above the 98th centile (+2.05 SD), and severe obesity at or above the 99.6th centile (+2.68 SD). Clinical judgement should be used when interpreting BMI below the 91st centile, as children may still have central adiposity despite a lower BMI.
Additionally, waist-to-height ratio is recommended to assess central adiposity in children and young people. A waist-to-height ratio under 0.5 is considered healthy, 0.5 to 0.59 indicates increased health risk, and 0.6 or more indicates further increased health risk. This measure applies across sexes and ethnicities and helps identify risks such as type 2 diabetes, hypertension, and cardiovascular disease.
Before taking measurements, it is important to ask the child or young person and their family or carers for permission and to ensure discussions are sensitive and non-judgemental. Suitable opportunities for measurement include routine health checks and non-urgent appointments.