A DEXA scan is a quick and painless procedure that involves lying on your back on an X-ray table so that an area of your body can be scanned.
No preparations are needed before having a DEXA scan. Depending on the part of your body being scanned, you may be able to remain fully clothed. However, you will need to remove any clothes that have metal fastenings. In some cases, it may be necessary for you to wear a gown.
Having a DEXA scan
Unlike a magnetic resonance imaging (MRI) scan, a DEXA scan does not involve being enclosed inside a tunnel, so you will not feel claustrophobic.
Instead, the scan takes place on a flat X-ray table that you lie on on your back. You will need to keep very still during the scan so that the images produced are not blurred.
The scan will usually be carried out by a radiographer (a specialist in taking X-ray images). As the scanning arm is slowly moved over your body, a narrow beam of low-dose X-rays will be passed through the part of your body being examined.
This will usually be your hip and lower spine to check for osteoporosis (weak and brittle bones). However, as bone density varies in different parts of the skeleton, more than one part of your body may be scanned.
Some of the X-rays that are passed through your body will be absorbed by tissue, such as fat and bone. An X-ray detector contained in the scanning arm will measure the amount of X-rays that have passed through your body. This information will then be used to produce an image of the scanned area.
A DEXA scan usually takes five minutes or less, depending on the area of your body being examined and whether you are having a central or peripheral scan (see DEXA scans).
During a peripheral scan, a small, portable device will be used to scan an area of your body such as your forearm, heel or hand. You will be able to go home immediately after having a scan.
Your results
A DEXA scan compares your bone density with the bone density of a young healthy adult or an adult of your own age, gender and ethnicity.
The difference is then calculated as a standard deviation (SD), which is a measure of variability based on an average or expected value.
The difference between your measurement and that of a young healthy adult is known as a T score, and the difference between your measurement and that of someone of the same age is known as a Z score.
The World Health Organization (WHO) classifies T scores as follows:
- Above -1 SD is normal
- Between -1 and -2.5 SD is classed as osteopenia
- Below -2.5 SD is classed as osteoporosis
If your Z score is below -2, your bone density is lower than it should be for someone your age.
Although bone mineral density (BMD) readings provide a good indication of bone strength, the results of a DEXA scan will not necessarily predict whether a fracture is likely to occur.
For example, someone with low bone density may never break a bone, whereas someone with average bone density may have several fractures. This is because other factors, such as age, sex, or previously having a fall, will also determine your susceptibility to experiencing a fracture.
Therefore, your doctor will consider all of your individual risk factors before deciding whether treatment is necessary.
