Dual-energy X-ray absorptiometry, or DEXA, is considered the gold standard for measuring bone mineral density and is also used to analyze body composition. But how accurate is this scan? Read on to learn more about the accuracy and precision of DEXA.

How does the DEXA scan work?

The DEXA scan works by sending two low-dose X-rays at different frequencies. These X-ray beams are absorbed differently by soft tissues and your bones. For that reason, DEXA can provide deep insight into a person’s body composition, such as adipose tissue, lean muscle, and bone mineral density.

The scan is quick and painless. It can last up to 15 minutes, but newer machines can take as little as two minutes. During the scan, you lie on a table which has a C-arm attached. The arm moves over your body to scan it, and a narrow beam of low-dose X-rays passes through the part of the body being examined.

Is the DEXA scan accurate?

The short answer is yes. The DEXA scan is not only accurate but also the gold standard. The standard error of measurement for the DEXA scan is 2.5% to 3.5%, whereas the error for other common methods can be up to 20%.

Various studies explored the efficacy and accuracy of DEXA. One paper from the journal Bone focused on 30 years of DEXA and reviewed its principles in soft tissue analysis, and other aspects. The paper confirms that DEXA is the preferred method for bone and body composition measurements. Moreover, the fundamental nature of DEXA is its accuracy over different body sizes and body types. What makes DEXA so accurate is that it measures regional body composition by subdividing the body with well-defined cut lines. The same paper reports it’s easy to check that body measurement machines remain accurate within 0.5% change over decades of use.

One of the earliest papers involving DEXA and measuring body composition was published in the September 1990 issue of the American Journal of Clinical Nutrition. In this comparative study, DEXA was accurate in referencing materials of water and lard representing lean tissues and fat.

In their paper from Radiologia Brasileira, researchers confirmed that a DEXA scan can identify differences in density among bone mineral content, lean body mass, and fat mass. The authors explained that this imaging technique allows for the detection of adipose tissue with high accuracy. For that reason, it’s possible to calculate the percentage of body fat mass, and the android/gynoid fat ratio. Fat Mass Index (FMI) is particularly important because it is based on actual body fat and is, therefore, a better tool for assessing overweight and obesity unlike body mass index (BMI). BMI focuses on the total body weight of a person only.

The Brazilian journal paper also reported that modern DEXA machines also measure visceral adipose tissue (VAT), which is usually measured with computed tomography (CT) scan or MRI. The DEXA-based estimation of VAT correlates well with CT-based estimation and can be routinely used to assess a person’s body composition. This further confirms the accuracy of the DEXA scan.

One common use of DEXA is in sports to track fat percentage and muscle mass in athletes. A study from the Journal of Sports Sciences confirmed the accuracy of DEXA in measuring body composition among team sports athletes. More precisely, DEXA exhibited great precision in measuring bone mineral content, fat-free soft tissue mass, and acceptable reliability for fat measures.

DEXA accurately detects regional changes in obesity

While DEXA scan is often discussed in terms of bone mineral density, it is also widely used for measuring body composition. This scan can help people tailor their diet and training plans to lose weight and tackle overweight and obesity more efficiently.

The September 2019 issue of BJR Case Reports published a paper that explored body composition, DEXA scan, and obesity. The study showed that the most common anthropometric measures, such as BMI and waist circumference, were ineffective at documenting body composition changes, however the DEXA scan could detect regional changes. Researchers concluded that longitudinal DEXA measurements provide a comprehensive assessment of body compartments. The excellent accuracy of DEXA suggests this scan be utilized to modify the clinical approach or to explain unexpected changes in clinical parameters based on the standard anthropometric approach.

Since DEXA can detect regional changes in body composition, it provides better insight into a person’s health. People who are actively trying to lose weight can modify their approaches to reduce total body fat, especially visceral adipose tissue.

DEXA and other methods

Some studies compared the effectiveness of DEXA and other imaging techniques in providing accurate measurements. For example, a study from the journal Children compared total body fat estimated by bioelectrical impedance analysis (BIA) methods, such as the bathroom scale, to that of DEXA. BIA test measures body composition according to the rate at which electrical current travels through the body.

This study's subjects were 76 male and 70 female young football players. Results showed that BIA significantly underestimates the fat percentage. On the flip side, DEXA was a more objective and accurate method for assessing fat mass in athletes. Besides underestimating values, BIA wasn’t accurate in people of great volume or athletes. DEXA is a good way to overcome these challenges and deliver accurate insight into a person’s body composition.

The abovementioned study isn’t the only one to compare DEXA and other techniques. Another example is a study from Quantitative Imaging in Medicine and Surgery, which reported that there is a very good correlation between fat mass measured by DEXA and CT or MRI. That means DEXA is an effective technique for assessing body composition and should be considered the method of reference in clinical practice.

A study from the Journal of Applied Physiology showed that DEXA is comparable to CT in reliability and accuracy in determining abdominal obesity. In the study, DEXA demonstrated excellent accuracy in measuring total, fat, and lean body mass.

The above-mentioned study confirmed that DEXA's accuracy is comparable to that of other imaging tests. What makes a DEXA scan stand out is that it’s less expensive than CT or MRI. Plus, it doesn’t cause claustrophobia-like discomfort, which is often seen in MRI examinations. Not only is DEXA more affordable than MRI, but it’s also accurate and convenient.

Conclusion

DEXA scan is a go-to method for evaluating bone density and body composition. This post aimed to provide a deeper insight into the effectiveness and accuracy of DEXA and its mechanism of action. A significant body of evidence confirms the accuracy of DEXA in measuring both mineral density and body composition, including visceral adipose tissue.

In fact, DEXA's accuracy is comparable to that of other techniques. DEXA is accurate, reliable, noninvasive, and less expensive than other types of scans. Schedule your appointment for a DEXA scan at Fitnescity and get access to a personal dashboard where you can track your progress.