A. Pietrobelli et al., DUAL-ENERGY X-RAY ABSORPTIOMETRY - FAT ESTIMATION ERRORS DUE TO VARIATION IN SOFT-TISSUE HYDRATION, American journal of physiology: endocrinology and metabolism, 37(5), 1998, pp. 808-816
Dual-energy X-ray absorptiometry (DXA) is rapidly gaining acceptance a
s a reference method for analyzing body composition. An important and
unresolved concern is whether and to what extent variation in soft tis
sue hydration causes errors in DXA fat estimates. The present study ai
m was to develop and validate a DXA physical hydration model, and then
to apply this model by simulating errors arising from hypothetical ov
erhydration states. The DXA physical hydration model was developed by
first linking biological substance elemental content with photon atten
uation. The validated physical model was next extended to describe pho
ton attenuation changes anticipated when predefined amounts of two kno
wn composition components are mined, as would occur when overhydration
develops. Two overhydration models were developed in the last phase o
f study, formulated on validated physical models, and error was simula
ted for fluid surfeit states. Results indicate that systematic errors
in DXA percent fat arise with added fluids when fractional masses are
varied as a percentage of combined fluid + soft tissue mass. Three ind
ependent determinants of error magnitude were established: elemental c
ontent of overhydration fluid, fraction of combined fluid + soft tissu
e as overhydration fluid, and initial soft tissue composition. Small b
ut systematic and predictable errors in DXA soft tissue composition an
alysis thus: can arise with fluid balance changes.