DXA: Not Just for Osteoporosis

In the field of body composition assessment, DXA is an important tool which give estimates of fat, bone and lean masses. In clinical settings, measurements of bone density are the most commonly assessed to monitor the development of osteoporosis that occurs with aging in postmenopausal women. However, DXA is equally important for the measurement of soft tissues, both fat and lean but these measurements are rarely made in clinical practice. Conditions such as obesity and sarcopenia are also important to monitor.

For those with obesity, weight loss is recommended with even a 5-10% loss associated with better health outcomes. But during weight loss, both fat and lean masses are often lost. The loss of lean mass is typically seen with caloric restriction and with weight loss medications but is minimized when resistance training is added to a weight loss effort. We addressed this issue in our recent book, ACSM’s Body Composition Assessment:

“Weight loss in older adults can lead to significant decreases in both muscle mass and bone density. Therefore, it is important to measure changes in these two components using DXA as a measure of both bone density (hip and spine) and lean soft tissue of the arms, trunk, and legs. While the former is performed routinely as a screening for osteoporosis, the latter is not typically performed. This test is easy to perform and could be done at the same visit as the osteoporosis screening scan. Health care professionals would need some training in how to interpret the results, but this would give valuable information about whole-body lean mass changes that occur under a variety of conditions. With the wide availability of DXA in hospitals and clinics throughout the country, it is not difficult to obtain DXA scans on clients undergoing weight changes or with aging.”         -Practical Insights from (ACSM’s Body Composition Assessment pg 150)

Sarcopenia, like osteoporosis, is another age-related condition that could be monitored in clinical practice. The Oxford Dictionary defines sarcopenia as “loss of muscle tissue as a natural part of the aging process”. This seems to imply that this loss of muscle is an inevitable part of aging, which isn’t completely true. With resistance training and activity, muscle can be maintained at a level which can extend good functional ability in older adults. DXA is a great tool that can be used to monitor this loss and to track efforts to improve one’s muscle mass.

While there is disagreement about how to diagnose sarcopenia, the European Geriatric Medicine Society organized a Working Group to update the definition of sarcopenia and to determine criteria for diagnosing and screening for sarcopenia. These criteria are (1) low muscular strength, (2) low muscle quantity or quality, and (3) low physical performance. They suggest that presence of low strength indicates probable sarcopenia and the addition of low muscle quantity/quality confirms the diagnosis. The presence of all three would indicate severe osteopenia. DXA plays a role is determining the quantity of muscle while fairly simple field tests can be performed to determine strength and function.

In general, the medical approach to aging is to treat any metabolic condition that may be present and to use DXA for osteoporosis diagnosis, but not for monitoring body composition and sarcopenia. We advocate for the use of DXA to also follow the loss of lean mass in older individuals every one to two years which would be a greater marker of the aging process. For those with obesity where weight loss is recommended, tracking fat mass can be done using the results from the same scan. In summary, DXA can play an important role in tracking body composition changes over time to maximize health.

References:

Cruz-Jentoft AJ et al. (2019) Sarcopenia: revised European consensus on definition and diagnosis. Age Ageing. 2019 Jan; 48(1): 16–31.

Risoul-Salas V et al. Body Composition Applications. (2020) In Lohman TG & Milliken LA (Eds) ACSM’s Body Composition Assessment, pg 150, Human Kinetics, Champaign IL.