1. health and fitness
2. disease

What is a DXA?
Dual energy X-ray absorptiometry (DXA, previously known as DEXA) is a technique of measuring
body composition including bone mineral density (BMD), body fat and lean muscle mass.
What is DXA used to measure?
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Bone Mineral Density: used to diagnose osteopenia and osteoporosis and to calculate
osteoporotic related fracture risk.
Evaluation of clinical obesity: a major risk factor for type 2 diabetes, metabolic syndrome,
and cardiovascular disease.1
Abnormal patterns of fat distribution (lipodystrophy): a major complication of antiretroviral
treatments.2
Muscle loss and wasting (sarcopenia): shown to be highly predictive of functional disability
in the elderly.3
Muscle gain and distribution: employed in elite athletes and military recruits as a
benchmark for physical performance and muscular strength.4, 5
What information does the Discovery Advance Clinical DXA Body Composition Report provide?
Discovery Advanced Clinical reports provide information on fat and lean mass indices that are useful
in the management of a wide variety of abnormalities including clinical obesity, abdominal obesity,
lipodystrophy, and sarcopenia.
Follow-up scanning is an invaluable tool in tracking progress for exercise programming and clinical
management interventions.
Here is an example of a subject on a diet and exercise regime who was scanned four times over 5
months. Notice the significant changes in the subject’s fat (yellow) from the picture on the left
compared to the picture on the far right taken 5 months later.
DEXA SCAN SYDNEY
City Clinic on Jamison 32 Jamison Street Sydney NSW 2000
Tel: 02 9304 5083
Accuracy and Calibration
These days medical technology needs to be fast, accurate and reliable. Discovery body composition
results have been calibrated to a large multi-center study between DXA and several other body
composition techniques including deuterium dilution, hydrostatic weighing, and 4-compartment
models.6 The results of this study found that previous methods under-estimated body fat by 4-5 %,
while overestimating lean body mass by the same factor.
The Discovery advanced whole body scanners use the latest APEX software, which has now
incorporated this updated National Health and Nutrition Examination Survey Body Composition
Assessment (NHANES BCA) calibration.
Diagnostic Information and Reference Data
Diagnostic information is obtained by direct comparison to a gender and ethnicity specific reference
data developed from NHANES data released on the Centre for Disease Control website. The NHANES
body composition reference database represents one of the largest peer-reviewed studies ever
undertaken and assures reliable results for all body composition measures.7 The NHANES database
uses statistical analysis methods which account for “skewed” (non-symmetrical) distribution of body
composition measurements. What does this mean? It means greater accuracy, validity, and clinical
usefulness of results, than has previously been available. Competitive DXA systems do not account
for skewness and therefore the diagnostic scores they provide may be unreliable.
DEXA SCAN SYDNEY
City Clinic on Jamison 32 Jamison Street Sydney NSW 2000
Tel: 02 9304 5083
Summary and Conclusion
Body composition measurements are expanding into many areas of clinical medicine and research.
Accurate and reliable results and diagnostic information are imperative for effective patient
management and can only be obtained on properly calibrated instruments utilizing the most
comprehensive database. The Discovery Advanced Clinical Body Composition evaluation satisfies
these requirements and sets the industry standard against which all DXA instruments are measured.
Prepared by:
Thomas L. Kelly Senior Principal Scientist Hologic, Inc. on behalf of Dexa Scan Sydney
References
1. S.C. Smith, Jr., "Multiple risk factors for cardiovascular disease and diabetes mellitus," Am J
Med, 120 (2007), S3-S11.
2. M. Law, R. Puls, A.K. Cheng, D.A. Cooper and A. Carr, "Evaluation of the HIV lipodystrophy
case definition in a placebo-controlled, 144-week study in antiretroviral-naive adults,"
Antivir Ther, 11 (2006), 179-86.
3. R.N. Baumgartner, K.M. Koehler, D. Gallagher, L. Romero, S.B. Heymsfield, R.R. Ross, P.J.
Garry and R.D. Lindeman, "Epidemiology of sarcopenia among the elderly in New Mexico,"
Am J Epidemiol, 147 (1998), 755-63.
4. A.R. Josse, J.E. Tang, M.A. Tarnopolsky and S.M. Phillips, "Body composition and strength
changes in women with milk and resistance exercise," Med Sci Sports Exerc, 42 1122-30.
5. M. Malavolti, N.C. Battistini, M. Dugoni, B. Bagni, I. Bagni and A. Pietrobelli, "Effect of
intense military training on body composition," J Strength Cond Res, 22 (2008), 503-8.
6. D.A. Schoeller, F.A. Tylavsky, D.J. Baer, W.C. Chumlea, C.P. Earthman, T. Fuerst, T.B. Harris,
S.B. Heymsfield, M. Horlick, T.G. Lohman, H.C. Lukaski, J. Shepherd, R.M. Siervogel and L.G.
Borrud, "QDR 4500A dual-energy X-ray absorptiometer underestimates fat mass in
comparison with criterion methods in adults," Am J Clin Nutr, 81 (2005), 1018-25.
7. T.L. Kelly, K.E. Wilson and S.B. Heymsfield, "Dual energy X-Ray absorptiometry body
composition reference values from NHANES," PLoS One, 4 (2009), e7038.
DEXA SCAN SYDNEY
City Clinic on Jamison 32 Jamison Street Sydney NSW 2000
Tel: 02 9304 5083