What is a DEXA Scan?
Dual energy x-ray absorptiometry, otherwise known as a DEXA scan, is a type of x-ray that measures the density and strength of your bones. It is used to estimate the extent of bone loss, diagnose osteoporosis or measure how well treatment for osteoporosis is working. They are the most accurate test for measuring bone loss, measuring within 2-4% precision.
How does a DEXA Scan work
DEXA scans use a much lower frequency or amount of radiation compared to x-rays. They use two x-ray beams that are absorbed by both soft tissue such as muscle and ligaments, and bones. Different equations are then used to calculate your bone mineral density – by subtracting the soft tissue absorption value, and using the bone tissue value to determine fracture risk, as fragile bones are more likely to break. Your bone density value is then compared to population data – to someone of the same sex, age and ethnic background to you, which will then give you an estimate of your risk of broken bones or fractures in the future.
What is Bone Mineral Density?
Bone Mineral Density (BMD) is the amount of minerals, mainly calcium and phosphorus, with small amounts of magnesium, in your bones. The denser your bones, or the more calcium detected, the stronger they are. When a DEXA scan is performed, the x-ray beams are measuring the calcium content and other minerals in your bones. It is important not to take calcium supplements 24 hours before a DEXA scan, as this will not give an accurate result of your bone density.
When you have a DEXA scan, the hip and lower spine are the sites measured, as the hip BMD is the most reliable in predicting hip fracture risk, and spinal BMD is used for monitoring treatment for osteoporosis. The spine, hip and forearm are measured by DEXA as they are common sites of fractures due to osteoporosis. The World Health Organisation (WHO) have recommended that DEXA is the most reliable technique for assessing BMD in menopausal women.
Why would you need a DEXA Scan?
There are three main reasons you would need to have a DEXA Scan to check your bone health:
- You went through early menopause – before the age 45 years
- You are in the later post menopause years, 70 years or older
- There is osteoporosis in your family
Other risk factors include:
- Significant weight loss or being underweight
- Being physically inactive
- Smoking
- Some drugs
- Alcohol – consuming more than 2 standard drinks per day
- Family history of hip fracture
- Low exposure to sunlight – leading to low Vitamin D levels
It is important to note that age is the strongest predictor of fracture risk.
What do you need to do to get a DEXA scan in Australia?
In Australia, you need to get a referral from your GP, family doctor or specialist. The referral your doctor will give you will be for a radiology centre that have a DEXA Scan machine to perform your test. In some cases, a Medicare rebate may be applicable, you can get up to date information about this on the Healthy Bones Australia website.
If you are concerned about your bone health or risk of osteoporosis, please discuss this with your doctor.
References
1. Capital Radiology, Bone Densitometry – What is a bone densitometry scan? https://www.capitalradiology.com.au/bone-density-scan
2. Choosing Wisely, Bone Density Tests https://www.choosingwisely.org/patient-resources/bone-density-tests/
3. Healthline, What is a DEXA Scan? https://www.healthline.com/health/dexa-scan#purpose
4. Healthy Bones Australia, About Bone https://healthybonesaustralia.org.au/your-bone-health/about-bones/
5. Healthy Bones Australia, Osteoporosis Diagnosis https://healthybonesaustralia.org.au/osteoporosis-you/diagnosis/
6. Mayo Clinic, Patient care and Health Information, Bone Density Test
https://www.mayoclinic.org/tests-procedures/bone-density-test/about/pac-20385273
7. Newman T, Medical News Today, Bones: All you need to know. Jan 11 2018 https://www.medicalnewstoday.com/articles/320444
8. Shue A & Diamond T, Bone mineral density: testing for osteoporosis, Australian Prescriber, 2016;39:35-9
9. Wikipedia, Dual-energy X-ray absorptiometry https://en.wikipedia.org/wiki/Dual-energy_X-ray_absorptiometry
