There are several caveats that arise as DXA is used in adolescents. A pediatric normative database must be used to interpret properly the measurement for either bone mineral content or BMD. The normative data must have been generated on a similar instrument58,59 and should account for sex58 and ethnicity,60,61 as each can influence bone mass. Since the z score is based on chronologic age, “correcting” the BMD for an adolescent with a delayed bone age (interpreting for that age) can be a helpful maneuver to avoid the overestimation of skeletal deficits.17,62 Even with appropriately matched databases and age adjustment, DXA does not adequately account for the influence of bone shape and size on its measurements.17,63- 65 In essence, DXA estimates bone mineral content by measuring the “shadow” cast by bone within a fan-shaped x-ray beam. This shadow is influenced not only by the composition of the bone, but its depth, which is not measured, and the distance of the bone from the beam.63,66 Attempts to correct for these limitations include obtaining 2 orthogonal scans (ie, anteroposterior and lateral), mathematical formulas to estimate volumetric BMD (eg, bone mineral apparent density),67,68 and more advanced regression models,69,70 none of which have been adopted uniformly. The bones of an adolescent are also changing continuously because of growth, which only further complicates the BMD interpretation.