Estimates of the precision of total and regional soft tissue body composition by dual-energy X-ray absorptiometry in persons with chronic spinal cord injury

Abstract

Introduction In both the clinical and research setting, the total body dual energy X-ray absorptiometry (DXA) scan is widely employed to measure longitudinal changes in fat tissue mass and lean tissue mass of the total body and regional areas in persons with spinal cord injury (SCI). Knowledge of the precision error is essential due to less than optimal limb positioning (i.e., joint contracture and spasticity) that could confound the reliability of body composition measurements. Objective The objective of this prospective observational study was to determine the short- and long-term reliability of total and regional soft tissue body composition assessments from a DXA total body scan in persons with motor-complete SCI. Methods Twenty-four individuals with SCI completed within day precision testing by repositioning study participants between scans (short-term precision error). An additional and separate cohort of 22 individuals with motor-complete SCI were scanned twice on a GE-Lunar Prodigy scanner separated by a 4-week interval (long-term precision error). To quantify precision error, the root mean square coefficient of variation percent (RMS-CV%) values and the inter-class correlation coefficient (ICC) values for the total body and regional areas (arms, legs, trunk, android, and gynoid regions) for all body composition variables [% fat mass, fat mass (kg), lean mass (kg), and total mass (kg)] were calculated and are presented. Results For all soft tissue body composition variables, the short-term precision assessment revealed the highest RMS-CV% from the body composition variables did not exceed 5.6%, 2.7%, 3.8%, 3.5%, 5.8% and 2.3% for arms, legs, trunk, android, gynoid, and total body, respectively. In the long-term precision assessment, revealed the highest RMS-CV% from the body composition variables did not exceed 6%, 3%, 4.4%, 6.7%, 3.4% and 1.96% for arms, legs, trunk, android, gynoid, and total body, respectively. To support the long-term precision error assessment, the interclass-correlation coefficient in the long-term precision group demonstrated excellent linear agreement between repeat scans for all regions (r ≥ 0.95). Conclusion Precision error of the total body and regional soft tissue body composition variables were similar to that reported in the non-disabled population. These findings support the use of DXA as a reliable method to assess longitudinal changes in the total body and regional areas from various pharmacological and therapeutic interventions in persons with SCI.