Bone Densitometry is a measure of the density of bone. Bone densitometry uses the rate of transmission of radiation through bone to detect the presence and degree of osteoporosis and other disorders of bone minerali-sation. Bone of reduced mineral density transmits radiation faster than normally dense bone. Several techniques are used. In single photon absorptiometry (SPA) the forearm is immersed in a water bath and bone density calculated from the rate at which radiation moves from one side of the bath to the other. This test is noninvasive and exposes the body to less radiation than does an ordinary CHEST X-RAY.

In dual photon absorptiometry (DPA) and quantitative computer tomography (QCf), the rate of movement of radiation through bone is mea-sured to calculate its density. These techniques can be used for less accessible sites, such as the spine and hip. DPA and QCF need costly equipment that is at present available only in special centres for the study of bone density.

Risks

• There are no particular risks associated with either of these tests.
• Fainting or feeling lightheaded.
• Occasionally minor bruising may occur at the site where the blood was taken.
• Excessive bleeding.
• Multiple punctures to locate veins.

How is a blood test normally done?

• The vein used for blood sampling is usually on the inside of your elbow or back of your wrist.
• The skin over the vein is usually cleaned with an antiseptic wipe.
• A needle is then inserted into the vein through the cleaned skin. The needle is connected either to a syringe, or directly to blood sample bottles.
• When the required amount of blood is taken, the needle is removed. A sticky plaster may be put on. The blood is placed in bottles.

Preparation

• There is no specific physical preparation for the blood test.
• Before the blood test, the patient must not eat or drink for four hours.