A B C D E F G H I J K L M N O P R S T U V W

BONE DENSITOMETRY - DEXA SCAN

What is Bone Densitometry ?

It is quite an accurate method of measuring the calcium content (or density) of bones using low dose x-rays. The amount of calcium in a bone gives some idea of how likely it is to fracture at a later date. If the density is low, then there is a greater chance of fracture.

Why is Bone Densitometry being performed ?

In both women and men, bone is at its strongest at about age 25 to 30. From then onwards the bones lose strength partly due to ageing: they contain less and less calcium. There are big differences between people in the rate at which they lose calcium. Women are at particular risk after their menopause. The fall in female hormone levels itself weakens the bones over a period of years. The other reasons for losing more calcium than usual are explained in the leaflet on osteoporosis. Osteoporosis means that the bones have such reduced levels of calcium, that you are at risk of breaking them. Such fractures may affect particularly the spine, the hip or the wrist.

Mostly, densitometry is carried out as a form of screening. There should be a good reason for doing this screening test. It may be considered if there is an early menopause, absence of periods, or known low female hormone levels. In men and women, steroid tablet treatment, thyroid or parathyroid overactivity and chronic kidney disease are the main reasons. Some doctors consider that it should also be done if you have a family history of osteoporosis, and particularly if you are also of lean build. You may have back pain or have sustained a fracture already. Your doctor may then suspect that osteoporosis is part of the cause. In this case, checking your bone density will also help.

Preparations needed for Bone Densitometry

No preparation is necessary. You can eat and drink normally before the test.

What Happens during Bone Densitometry

You will be asked to remove any clothes with metal fastenings or zips which are over the hips or lower back. You will then be asked to lie on the examination table. The technician or radiographer carrying out the test will make you comfortable with pillows. Most densitometers measure the density in two areas of the body the vertebrae of the lower spine and one hip. You will have to lie in the same position for 5 minutes for each assessment. The whole test takes 15 to 20 minutes. The measurements are made with a mechanical arm which moves slowly above the body. You will feel nothing during the test. The measurements are checked by the technician or radiographer who usually remains in the room throughout the test. When the test is over, you can sit up and leave the room. The information obtained by the bone densitometer is processed by a computer which then prints out the result of the test.

Possible Complications during Bone Densitometry

The test is safe and there are no complications. It uses a very small dose of x-rays, about one-tenth of that received from a standard chest x-ray. It can therefore be repeated many times without risk.

After Bone Densitometry

There are no long-term effects from the test. You can eat and drink normally, engage in normal physical activity, and come into normal contact with people. Your doctor will be sent the results as a group of numbers. The lower the number, the less dense the bone. There will often be a graph or chart attached. This shows you and your doctor your bone density for the hip and spine. This will allow you to compare your result with the normal range expected for other people in your age group and sex. If the level is below the ideal for your age, it tells the doctor that you may be more likely than other people to fracture bones in the future. We now have ways of slowing down and even improving the strength of bones. Therefore it is better to pick up the tendency as soon as possible. You may be told about your T-score. This compares your bone density to that of healthy bones in people aged approximately 30. Above a "score" of minus 1, no action is usually advised. Between minus 1 and minus 2.5, the term osteopenia is often used. This indicates a bone density between normal and definite osteoporosis. You may be recommended treatment at this level. Below minus 2.5, you will be considered to have osteoporosis, and it is almost certain that you will be offered treatment. If reduced bone density was found, it is likely that the test will need to be repeated at a later date. This is firstly because a reduced bone density does not tell the doctor exactly how fast you are losing calcium. Doing a repeat test a year or two later will provide this information. If your doctor has prescribed treatment after your first scan, it will also help him or her to see whether the treatment has been effective. Repeating the test earlier than one year later is not worthwhile. The density of bones changes quite slowly. Also, the method is not sensitive enough to pick up very small changes. For this reason, it is also a good idea to have any repeat tests done on equipment of the same manufacturer.

If Bone Densitometry is not performed

DEXA bone densitometry is probably the best test for picking up a tendency to osteoporosis. If the test is not carried out, there is no easy alternative, although ultrasound and other techniques are being developed. Ordinary x-ray pictures are not sufficiently sensitive: more than 50% of calcium needs to be lost from a bone before it will show any change on an ordinary x-ray. An alternative (older) test, which can be painful and is probably no more accurate, can be done. It involves removing a piece of bone from the hip and examining it under a microscope. Because early osteoporosis usually gets worse and can be treated, it does pay to pick it up early.