The Devil Is Always In The Detail

In 2006 we opened as the first commercial DEXA measurement service in Australia specialising in body composition measurement. Between 2006 and 2013 we were essentially the only body composition practice in Sydney. There are now 6 operating DEXA practices “specialising” in body composition measurement in Sydney and others interstate.

DEXA have two functions:

1.To measure bone mineral density and;

2.To measure soft tissue (body composition).

The two most well utilised bone densitometers in the bone density area in Australia are GE (Lunar, IDEXA) and Hologic (Horizon,Discovery). Both companies have been around for over 20 years. There is also a new comer in the market in Australia, a brand called MediLink (MedixDR);

With DEXA measurement as an industry being in its infancy, competition is only a good thing and encourages efficiencies in price, product and service. At MeasureUp our ethos has always been to provide accurate data to identify progress and change with an individuals’ body. The key word here is accurate. We know the difference in our product, price and service but it is very important that the consumer also knows the difference between the players in the field, so to speak.

Over the past year since a number of other clinics have opened, we have had many people revisit MeasureUp with scans completed on other DEXA scanners. Compared to the results produced by our DEXA (Hologic Discovery) there is evidence of over-estimating and under-estimating both body fat and muscle mass. The difficulty here is that you as the customer does really not know what to believe with respect to their results. There is a simple solution: ask the DEXA practice you attend if they undertake a specific calibration of their DEXA using a specialised body composition phantom.  In fact, a position paper published by the International Society for Clinical Densitometry in 2013 stated that GE and Norland have not altered their calibration of fat and lean mass in the past 20 years and few details exist on what these systems are calibrated to. Unfortunately comparisons of these densitometers with other imaging methods are no more useful in attaining accuracy because these other methods have not been calibrated to absolute standards either.

What does MeasureUp do differently?

There are two calibration procedures that must be undertaken by DEXA scanning facilities:

1. A daily calibration procedure.

This daily procedure is known as a quality control or quality assurance procedure (using a smaller phantom). This is simply a daily test to make sure the DEXA is operating properly (within its limits) and ensures the validity and accuracy of the data that the DEXA provides you, the paying customer. If calibration is not completed by your DEXA facility then the data is no more accurate then throwing darts in the air and seeing where they land.

2. Calibration of the DEXA itself using a known constant.

MeasureUp employs its own specific Hologic body composition phantom. The phantom is 4 layered and weighs 30kg. It is made of aluminium bars to represent bone mineral and layers of low-density polyethylene and polyvinyl chloride to represent varying compositions of soft tissue. This is as close as the scientific community can get to mimic the X-ray properties of adipose (fat) and muscle tissue over a wide range of energies. Unfortunately these phantoms still cannot be used as an absolute reference standard but at least we are testing our DEXA with a known constant.

MeasureUp also employ university qualified staff who use evidence based research to recommend exercise and nutrition programs based on the accurate results the DEXA provides. Accurate data is one thing, but the ability to disseminate the data and provide solid recommendations based on science are just as crucial to the service we provide.

Next time you have a DEXA, Ask your DEXA facility if they calibrate their DEXA with a specific body composition phantom, this is the detail that differentiates accuracy from estimation. As they say, buyer beware.

Hangartner et al. The Official Positions of the International Society for Clinical Densitometry: Acquisition of Dual-Energy X-Ray Absorptiometry Body Composition and Considerations Regarding Analysis and Repeatability of Measures. Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health, vol. 16, no. 4, 520-536, 2013.

 

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