Measurement precision of body composition variables using the Lunar DPX-L densitometer

The objective of the study was to determine the precision of total and regi onal body composition measurements from a total-body scan using dual-energy X-ray absorptiometry (DXA). This is critical information necessary to dete rmine the smallest change from baseline that could be detected with statist ical significance when conducting longitudinal measurements of body composi tion variables in an individual. Twenty volunteers were scanned once each d ay for 4 consecutive days using a Lunar DPX-L densitometer and manufacturer -supplied software (version 1.3z). Coefficients of variation (CV, %) derive d from data using the (preferred) extended research mode of analysis were 0 .62, 1.89, 0.63, 2.0, 1.11, 1.10, and 1.09% for total-body bone mineral den sity (BMD), total percentage fat, total body tissue mass, fat mass, lean ma ss, bone mineral content (BMC), and total bone calcium, respectively. Regio nal measurements (arm, leg, trunk, pelvis, and spine) were less precise tha n total-body measurements, with CVs in the range of 1% to 3% (but fat mass for arms was 4.26%, trunk 3.08%, BMC 3.65%). Small but statistically signif icant differences in mean values for most body composition variables were f ound when data were compared between extended and standard modes of analysi s. Inconsistent use of analysis mode in a cohort or when following a patien t longitudinally may negatively affect precision. We conclude that the meas urement precision of total- and regional-body composition variables was gen erally comparable to the precision limits typically associated with lumbar spine and proximal femur BMD data.