title: QDR 4500A DXA overestimates fat-free mass compared with criterion methods.
abstract: This study evaluated the accuracy with which the dual-energy X-ray absorptiometer (Hologic QDR 4500A) measured fat-free mass (FFM), fat mass (FM), and hydration of FFM. In a study of 58 men and women (ages 70-79 yr), the QDR 4500A was found to provide a systematically higher estimate of FFM and lower estimate of FM than a four-component model of body composition. A correction factor from this study was developed and applied to two other samples (n = 13 and 37). We found mean corrected levels of FFM and FM to be equivalent to that obtained by the four-component model or total body water. In addition, the hydration of the corrected FFM was closer to the established hydration level in adult samples and that obtained from the four-component model. These findings suggest that the current calibration of the fan-beam system of the Hologic QDR 4500A provides an overestimate of FFM and underestimate of FM compared with reference methods.
authors.affiliation: Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38105, USA. ftylavsky@utmem.edu
authors.forename: Frances
authors.initials: F
authors.lastname: Tylavsky
authors.forename: Timothy
authors.initials: T
authors.lastname: Lohman
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Blunt
authors.forename: Dale A
authors.initials: DA
authors.lastname: Schoeller
authors.forename: Thomas
authors.initials: T
authors.lastname: Fuerst
authors.forename: Jane A
authors.initials: JA
authors.lastname: Cauley
authors.forename: Michael C
authors.initials: MC
authors.lastname: Nevitt
authors.forename: Marjolein
authors.initials: M
authors.lastname: Visser
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
mesh_terms: D015502:Absorptiometry, Photon / Q000295:instrumentation / Q000592:standards*; D000368:Aged; D000375:Aging / Q000502:physiology; D000465:Algorithms; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D002138:Calibration; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D012016:Reference Values