In response.

We welcome the letter by Prof Barr.1 Indeed, we consider our study on a sample of adolescent survivors of ALL2 to provide empirical support for the prediction made in a study by Webber et al3: interpreting dual energy x-ray (DXA) bone health data requires caution. In particular, failure to adjust DXA bone mineral density (BMD) data for body size risks erroneous judgments about bone health, which could be clinically important,3 particularly in children and adolescents with chronic disease.1,2 Although DXA is a valuable component of the assessment of bone health,4 and knowledge of the need to adjust BMD values appropriately for body size is increasing, this point is not as widely known as it should be at present.2 Barr1 also highlights the potentially valuable role for DXA in the assessment of body composition. We agree that DXA has great potential as an accurate and precise measure of fat and lean mass in children and adolescents. However, DXA is not a “gold standard” for body composition measurement,5 and we would add that caution is also necessary here. Different combinations of DXA hardware and software are likely to have different accuracy, and the errors inherent in DXA estimates of body composition can be very large.6 In summary, DXA, when used appropriately, can be extremely valuable in the assessment of both bone health and body composition, and the technique can inform both research and clinical management.