Note: the information below is a general guide only. The arrangements, and the way tests are performed, may vary between different hospitals. Always follow the instructions given by your doctor or local hospital.
What is a DEXA scan?
DEXA stands for 'dual-energy X-ray absorptiometry'. DEXA (also sometimes known as DXA) is a test that measures the density of bones. Density means how much of something there is in a certain amount of space. The denser the tissue, the less X-rays pass through. Air and water are less dense than solid things such as bone. This is because the particles which make air and water are not held closely together. In general, the more dense the bone, the stronger it is, and the less likely it is to break (fracture).
There are two different types of DEXA scanning devices:
- Central DEXA devices are large machines that can measure bone density in the centre of your skeleton, such as your hip and spine.
- Peripheral DEXA devices are smaller, portable machines that are used to measure bone density on the periphery of your skeleton, such as your wrist, heel or finger. These are mainly to get an idea about whether further tests are needed, as they are not as accurate as the larger DEXA machines.
How does a DEXA scan work?
A DEXA scan uses low-energy X-rays. A machine sends X-rays from two different sources through the bone being tested. Bone blocks a certain amount of the X-rays. The more dense the bone is, the less X-rays get through to the detector. By using two different X-ray sources rather than one it greatly improves the accuracy in measuring the bone density.
The amount of X-rays that comes through the bone from each of the two X-ray sources is measured by a detector. This information is sent to a computer which calculates a score of the average density of the bone. A low score indicates that the bone is less dense than it should be, some material of the bone has been lost and it is more prone to fracture.
How is a DEXA scan done?
You lie on your back on a couch and are asked to keep still while an X-ray detector (the 'scanner') comes over the area to be tested. An X-ray machine fires X-rays towards the detector. The bones commonly scanned are the bones of the back (the vertebrae), hip and wrist. The scan usually takes between 10 and 20 minutes, depending on which part of your body is being examined and whether a central or peripheral scanner is being used. Peripheral scanners are available in some GP surgeries and can be used to check the bone mass density of the heel, wrist or finger.
By Nick Smith photography (ALSPAC web site), via Wikimedia Commons.
DEXA scans use a very low level of X-ray radiation. This means it is safe for the technician doing the scan to stay in the room with you. (In standard X-ray tests, the technician has to stay behind a protective screen.)
You do not need to do any special preparation prior to a DEXA scan.
Who should have a DEXA scan?
A DEXA scan may be advised if you have had a fracture of a bone after a minor injury. It may also be advised if you are considered at increased risk of 'thinning' of the bones (osteoporosis) and therefore at increased risk of having a fracture in future. You can read about what might make you at increased risk in the leaflet called Osteoporosis.
If your doctor thinks you have risk factors for osteoporosis, they may use a risk calculator such as one called FRAX®. This gives an idea of how likely you are to fracture your bones after a minor knock. If your risk is at a medium level, your doctor would then arrange a DEXA scan. This enables them to gain a clearer picture of your risk and then to decide whether you need any treatment.
Further reading and references
Clinical guideline for the prevention and treatment of osteoporosis; National Osteoporosis Guideline group (NOGG) 2017
Osteoporosis: assessing the risk of fragility fracture; NICE Clinical Guideline (August 2012, updated February 2017)
Management of osteoporosis and the prevention of fragility fractures - A national clinical guideline; Scottish Intercollegiate Guidelines Network - SIGN, (March 2015)
Guideline for the diagnosis and management of osteoporosis in postmenopausal women and men from the age of 50 years in the UK; National Osteoporosis Guideline Group (updated 2014)
Bisphosphonates for treating osteoporosis; NICE Technology Appraisal Guidance, August 2017
Denosumab for the prevention of osteoporotic fractures in postmenopausal women; NICE Technology Appraisal Guidance, October 2010
Avenell A, Mak JC, O'Connell D; Vitamin D and vitamin D analogues for preventing fractures in post-menopausal women and older men. Cochrane Database Syst Rev. 2014 Apr 144:CD000227. doi: 10.1002/14651858.CD000227.pub4.
Black DM, Rosen CJ; Clinical Practice. Postmenopausal Osteoporosis. N Engl J Med. 2016 Jan 21374(3):254-62. doi: 10.1056/NEJMcp1513724.
Hip fracture: management; NICE Guideline (June 2011, updated May 2017)
Management of hip fracture in older people; Scottish Intercollegiate Guidelines Network - SIGN (June 2009)
Vitamin D and health; Scientific Advisory Committee on Nutrition (July 2016)
Sunlight exposure: risks and benefits; NICE Guidance (February 2016)
Santesso N, Carrasco-Labra A, Brignardello-Petersen R; Hip protectors for preventing hip fractures in older people. Cochrane Database Syst Rev. 2014 Mar 31(3):CD001255. doi: 10.1002/14651858.CD001255.pub5.
Several people have posted recently that they have been able to reverse their measured (DXA scan) bone thinning through natural means - nutrition, appropriate supplements and exercise. It would be...Anhaga
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