Dual-Energy X-Ray Absorptiometry Interpretation: A Simple Equation for Height Correction in Preteenage Children

Abstract

Dual-energy X-ray absorptiometry (DXA) results, even when corrected for age, gender, and ethnicity, can lead clinicians to erroneously diagnose osteoporosis in short healthy children and underdiagnose osteoporosis in tall children. We derived 2 simple equations for preteenagers <Tanner 3 to “height-correct” any DXA instrument having pediatric reference ranges. Our equations to find “height-age” (HA) are based on Center for Disease Control and Prevention growth tables. The equations calculate HA; i.e., the age a child would be if he/she were 50th percentile for height. For girls (ages 2–12yr, heights 85–151cm): HA(yr)=21.53+0.447×height(cm)−6.2415×height(cm). For boys (ages 2–13yr, heights 86–156cm): HA(yr)=8.23+0.3264×height(cm)−3.7×height(cm). Next, we applied our 2 equations to DXA results acquired from 102 children with untreated hypophosphatasia (HPP), a disorder that impairs bone mineralization and compromises height. Our height-adjusted bone mineral density and bone mineral content Z-scores were concordant with the multistep methods of Zemel et al for the overlapping age ranges. Thus, we validated, using HPP patients, our equations (and, by extension, the visual inspection method) and the method of Zemel et al for use in children in bone disease. Our equations remove a height-effect for both pediatric spine and total hip DXA Z-scores. They help to correct for bone size in American children <Tanner 3 without using growth tables or statistical software, apply to all DXA instruments, and evaluate even young children. Similar equations could be derived for any pediatric population for which sufficient growth data are available.