1. As a physician, what does the body composition analysis by DEXA tell you that the BMI and your own eyes do not?
BMI is the minimum measurement for evaluating the overweight and obese patient, ultimately a reflection of body weight. Body weight is not nearly as important as the composition of that weight when considering health and disease of a patient.
Body composition analysis measures proportions of fat and lean mass in the body, rather than just the combined weight of all tissues. It can help identify patients who have increase in visceral fat (associated with increased risk of heart disease and diabetes) but not an increase in total body fat, making BMI a poor representation of their fitness. Body composition analysis is also accurate in monitoring the of body fat loss and muscle growth during weight management and fitness programs.
2. How does the DEXA scan results compare with other methods used to tell people about their body composition? Bio impedance? Bod Pod (Air displacement plethysmography), skinfolds, circumferences and some of the newer ultrasound measures?
Multisite testing of skinfold thickness is considerably less accurate than measurements of height or weight, particularly in obese subjects.
Waist circumference is a measurement of abdominal obesity and provides risk information that is not accounted for by BMI, as patients with increased waist circumference or “abdominal obesity” are at increased risk for heart disease, diabetes, hypertension, dyslipidemia, and nonalcoholic fatty liver disease. But as mentioned before, these methods are unable to accurately measure lean mass.
Bio impedance simple and widely used but has limitations. These tools convert impedance, which is a measure body water, into an estimate of fat. Variations in electrode placement can cause relatively large errors in the measurement of impedance and corresponding errors in the estimate of body water. Compared to DEXA, bio impedance measurements on average underestimate the body fat mass.
Bod Pod (Air displacement plethysmography) also has a small but significant underestimation of % body fat when there is a presence of excess heat, moisture, elevated body temperature, clothing and body hair in the BOD POD testing chamber, limiting the accuracy of and consistency of monitoring.
Ultrasound has also been a technology used to measure body fat with that does not involve radiation. Despite the advantages, there is a lack of standardized procedure and results are highly dependent on the skill of the operator. Further advances in this technique are required to minimize the limitations.
DEXA is generally the preferred method in a clinical setting when a more rigorous determination of body composition is needed. It has been validated against other techniques, uses a very low dose of radiation, and is relatively simple for the operator and patient to perform. It provides the highest accuracy and repeatability of subsequent testing
3. Are DEXA scans safe? How often would you recommend someone reassess their body composition?
Yes DEXA is safe. The effective radiation dose is a very low safe amount, significantly less than that of an x-ray
There are no absolute contraindications to performing DXA, though generally advise pregnant women to not get a DEXA scan
A body composition test is typically repeated every 3 months and can be safely repeated as often as once a month.
4. Why aren’t DEXA scans more common-readily available?
DEXA scans for body comp are generally not covered by insurance and are out of pocket expenses.
American College of Radiology. “ACR–SPR–SSR PRACTICE PARAMETER FOR THE PERFORMANCE OF DUAL-ENERGY X-RAY ABSORPTIOMETRY (DXA).” 2013.
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