Submitted to: International Journal of Body Composition Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/9/2009
Publication Date: 10/9/2009
Citation: Shypailo, R.J., Ellis, K.J. 2009. Longitudinal DXA Studies: Minimum scanning interval for pediatric assessment of body fat. International Journal of Body Composition Research. 7(3):117-122. Interpretive Summary: Obesity levels in the United States are increasing. Because of this, Dual-energy X-ray absorptiometry (DXA) is being used more often for measuring body fat (TBF). We wanted to see how soon DXA scans could be repeated to measure meaningful TBF changes in children. We did this by evaluating the precision of our instrument using a Hologic Delphi instrument (version 12.1). An Average-sized child should surpass the least significant change for TBF within a year, except at the very youngest or oldest ages. Waiting a minimum of 6-8 months before rescanning a child may be sufficient when monitoring TBF during pubertal growth, when children change most rapidly. Precision testing should be done with other machines in order to calculate accurate least significant change values for TBF.
Technical Abstract: The increased prevalence of obesity in the United States, has led to the increased use of dual-energy X-ray absorptiometry (DXA) for assessment of body fat mass (TBF) in pediatric populations. We examined DXA precision, in order to determine suitable scanning intervals for the measurement of changes in 38 children (ages 4-19 y), using a Hologic Delphi A (vers. 12.1). We calculated the root mean square standard deviation (SDRMS), percent coefficient of variation (%CV RMS), then the least significant change (LSC) at the 95% confidence interval for both SDRMS and %CV RMS. Normal growth trends were based on a cross-sectional set of DXA scans of 1410 children (ages 2-20 y). LSCSD for all children was 716 g and 1.4% for TBF and %Fat, respectively, while LSC%CV results were about 6% for both TBF and %Fat. For TBF, LSCSD was higher for girls than for boys (890 g vs. 575 g), while LSC%CV was higher for boys than for girls (7% vs. 5%). Short-term precision results suggest that, TBF changes of at least 890 g for girls and 575 g for boys are needed, in order to detect a true change at the 95% confidence level. An average-sized child should eclipse the LSCSD for TBF during most any year, except at the very young or the oldest ages. A minimal scanning interval of 6-8 months may be sufficient when monitoring TBF during the pubertal growth spurt. DXA facilities should consider doing their own precision testing in order to derive accurate LSC thresholds for BFG and %Fat for children.