Body composition measurement: the challenge in the unwell child

The assessment of body composition in the unwell child presents a significant clinical and technological challenge. The effect of disease adds to the complex series of changes in body composition that occur during normal growth and development. To assess the progress of disease or the effect of therapy, repeat measurements of body composition in a single patient may be desirable. However, repeat studies using some methods may not be appropriate due to the potential risks associated with repeated radiation exposure in this young age group. The ability to accurately detect changes in body composition between studies depends on the precision of measurement. Unfortunately, there may be a reduction in precision of measurement with smaller patients when the ability for detecting small changes is of particular relevance. Adequate and correctly timed fluid samples required for dilution studies may be difficult to obtain in the unwell infant and child. New equations or modification of 'adult' equations need to be devised to interpret raw data and these need to be validated in patients of different ages and sizes and in children with different diseases states. Specific challenges related to some common and uncommon paediatric diseases are discussed.