What is Dexa Scan & What is it Used For?

What is a DEXA Scan?

A dual-energy X-ray absorptiometry (DEXA) scan is a type of X-ray that measures the bone mineral density and potential bone loss. It is a high-precision form of X-ray and if a person’s bone density is lower for their age, then the DEXA scan helps in indicating the risk for bone fractures and osteoporosis.

What is a DEXA Scan?

When Was DEXA Scan First Used?

The DEXA scan was available commercially for the first time in 1987.(4)

Explain the Technique in DEXA Scan?

The technique in DEXA scan works by sending two beams of x-rays at different peak energy frequencies towards the target bones. The benefit of using two energy levels in a DEXA scan separates the images into two separate components, bone and soft tissue.

One peak energy frequency is absorbed by the soft tissue and the other peak frequency beam is absorbed by the bone. The bone mineral density is determined by subtracting the soft tissue absorption amount from the total absorption amount.

Which Parts Of The Body Does The DEXA Scan Focus On?

Typically a DEXA scan targets your hips and lower spine.(5)

How Safe is DEXA Scan?

DEXA is a non-invasive test, very safe, fast, and is also more accurate than a regular x-ray test.(3, 6, 7)

How Accurate is DEXA Scan?

While standard X-ray diagnostics that was used before the development of the DEXA scan were only able to assess bone loss that was over 40 percent. However, with DEXA scans, it is possible to measure bone loss within two to four percent precision.

Before the development of DEXA technology, the first sign of bone density loss was usually when an elderly broke a bone.

Why is DEXA Scan Considered More Accurate than a Regular X-Ray?

DEXA scan is more accurate than a regular x-ray because it can detect even the minutest changes in bone loss. DEXA scan also involves a low level of radiation, decreasing the risk of being exposed to radiation while undergoing an x-ray. DEXA scan is even more reliable than other methods of determining body fat percentage, such as underwater weighing.

A DEXA scan can also help doctors determine a patient’s body composition, such as the percentage of fat and lean muscle.

What Do The Results of a DEXA Scan Indicate?

Results of a DEXA scan can indicate to doctors the severity of bone loss, helping them understand the risk of developing a fracture.

The results of the DEXA scan, when used for assessing your body composition, may also help determine the level of visceral fat. Visceral fat is the fat the body stores around some of your internal organs.(1)

What is a DEXA Scan Used For?

A DEXA scan is most commonly used for determining whether a person’s bones are at risk of fracture and/or weak. Doctors also use the DEXA scan reports for diagnosing osteoporosis.

Osteoporosis is a condition that causes your bones to become thin and/or lose density. When your bones become thin, they are more fragile, making them more susceptible to fracture. Diagnosing whether a person has osteoporosis at an early stage prevents the condition from getting worse and also lowers the risk of fractures.

A DEXA scan is also used by a doctor for assessing whether or not your osteoporosis is progressing. After your first DEXA scan, your doctor will typically prescribe another scan within a year or two to understand whether there has been any change in your bone density. These DEXA scans can also help doctors determine the effectiveness of your prescribed osteoporosis treatment. Doctors take a call on whether your bone density is improving or worsening, or whether your bone density is the same.

Who Should Undergo DEXA Scan?

According to data from the National Osteoporosis Foundation, males over the age of 70 and females over the age of 65 should seriously consider having a DEXA scan. The frequency of these scans would depend varying on the results of your first scan.(2)

People who have osteoporosis and are receiving treatment may need to undergo a DEXA scan every one or two years.

Postmenopausal women who are younger than 65 and have other risk factors for low bone density, such as low body weight or using steroid medications, should also consider getting a DEXA scan. Medical experts recommend that females should undergo a DEXA scan at a much earlier age than men because women tend to lose bone density sooner than men.

When Will You Doctor Order a DEXA Scan?

Your doctor is likely to prescribe a DEXA scan in the following conditions:

  • If you break a bone after the age of 50.
  • If you are over the age of 65 and a woman.
  • If you are a man over the age of 70.

If you are a man between 50-59 years or a postmenopausal woman under 65 and have the below-mentioned risk factors:

Some of the risk factors for osteoporosis include:

  • Low body mass index.
  • Use of alcohol and tobacco.
  • Physical inactivity.
  • Some diseases, such as rheumatoid arthritis.
  • Use of corticosteroids and some other drugs.
  • Previous fractures.
  • A family history of osteoporosis.
  • Height loss of over an inch.

Explain About the DEXA Scan Procedure and its Duration?

There is no need for any particular preparation before taking a DEXA scan. You can continue to eat and drink as you normally would before undergoing the scan. However, for people who are taking calcium supplements, they will need to stop taking these supplements at least 24 hours before taking the DEXA scan.

The DEXA scan will be performed by an x-ray technician.(8) It is an outpatient procedure and the entire process will take only few minutes.(8) You will be done before you know it.

The DEXA apparatus has a flat padded table on which you will need to lie on. There is a movable arm above the table that holds an x-ray detector. The device that produces the actual x-ray is located below the table.

The X-ray technician will position you on the table and then place a wedge beneath your knees so as to flatten your spine or the wedge will be used to position your hip. The technician may also position your arm for the scanning procedure.

You will be asked to stay very still while the movable imaging arm above will move slowly across your whole body. The x-ray radiation level is also low enough that the technician will remain in the room along with you while operating the device.

Understanding the Results of DEXA Scan

Your DEXA scan reports will be analyzed by a radiologist and then given to you as well as your doctor within a few days.

The scoring system for a DEXA scan determines your bone loss as against that of a healthy young adult. These standards have been established by the World Health Organization. This is known as your T score.(8) The T score is the standard deviation between the average bone loss and measured bone loss. The scores from DEXA scan indicate the following:

  • A score of -2.5 and below means you have osteoporosis and a high risk for fracture.
  • A score between -1.1 and -2.4 means you have osteopenia and an increased risk of fracture.
  • A score of -1 or above is considered normal.
  • Sometimes, your results may also give you a Z score. This compares your bone loss to the bone loss of others in your age group.(8)
  • While the T score measures your relative risk, it is still not a sure shot prediction that you will definitely have a fracture.
  • Your doctor will help you understand your test results and then will discuss whether or not any treatment is required, and if so, what these treatment options are.
  • Your doctor is also likely to follow up with another DEXA scan in a period of two years to measure if there have been any changes in your bone density.

Outlook and Conclusion

If your DEXA scan results indicate that you have osteoporosis or osteopenia, then your doctor will go ahead and discuss potential treatment options with you and also advice on what you can do in order to remain healthy and slow down bone loss.

Treatment in this case simply involves small lifestyle changes towards a healthier lifestyle. You may be recommended to lose weight, practice balance exercises, strengthening exercises or weight-bearing exercises.

You may need to start supplements if your vitamin D or calcium levels are low.

For more severe osteoporosis, your doctor may recommend that you take some medication for strengthening your bones and also for reducing bone loss. However, before beginning any drug treatment, make sure that you are aware of any potential side effects of the medications.

Having a healthy lifestyle and starting medication for slowing down bone loss is a good way to ensure your health and longevity.

References:

  1. Carlson-Newberry, S.J. and Costello, R.B., 1997. Dual-Energy X-Ray Absorptiometry: Research Issues and Equipment. In Emerging Technologies for Nutrition Research: Potential for Assessing Military Performance Capability. National Academies Press (US).
  2. National Osteoporosis Foundation. (2019). Bone Density Test, Osteoporosis Screening & T-score Interpretation. [online] Available at: https://www.nof.org/patients/diagnosis-information/bone-density-examtesting/ [Accessed 15 Apr. 2019].
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2965908/
  4. https://www.ncbi.nlm.nih.gov/books/NBK233779/
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600106/
  6. https://www.ncbi.nlm.nih.gov/books/NBK519042/
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3891842/
  8. https://www.medicalnewstoday.com/articles/324553.php

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