Since we can't see inside our bones, often osteoporosis is not detected until after a fracture occurs. Bone density testing can help identify those with osteoporosis or who are at risk of osteoporosis before it occurs. If bone density tests are conducted over a period of years, the rate of bone loss or effectiveness of therapy can be determined. The following are ways bone density is measured and a description of each procedure:
- DXA (Dual Energy X-Ray Absorptiometry) is the most commonly used test for bone mineral testing. This can be used to measure the spine, hip, or total body. DXA is the most commonly used measurement, other than a bone ultrasound. DXA measures bone mineral content at significant sites of fracture such as the spine and hip. It is highly accurate with a precision up to one percent. DXA uses a low radiation dose, requires a short examination time, and patients experience minimal inconvenience.
- SXA (Single Dual Energy X-Ray Absorptiometry) is used to measure the wrist or heel. SXA figures bone mineral as it passes from a constant thickness of soft tissue or water bag into the bone. SXA is similar to DXA, but is not as accurate or widely used.
- P-DXA (Peripheral Dual Energy X-Ray Absorptiometry) measures the wrist, heel, or finger. P-DXA is a modification of DXA. If the hip or spinal bone is measured, P-DXA is not needed, only DXA is needed. P-DXA also uses very low doses of radiation, and the results are faster than conventional DXA measurements. P-DXA has limited usefulness (compared to DXA) for monitoring the effect of medication used to treat osteoporosis.
- DPA (Dual Photon Absorptiometry) measures the spine, hip, or total body. DPA uses a radioactive substance to produce radiation. DPA uses very low doses of radiation, also, however it has a slower scan time than other methods of screening.
- QCT (Quantitative Computed Tomography) is used only on the wrist. QCT is not usually recommended because it is expensive, uses higher radiation doses, and is less accurate than DXA, P-DXA, or DPA.
- Ultrasound uses sound waves to measure the heel, shin bone, or kneecap. It is one of the most commonly used measurements, along with DXA. It is less expensive and requires less time than most of the other screenings. Ultrasound is not accurate enough to be used to make a diagnosis, but is used for screening. Ultrasound has a high frequency sound that travels through the tissues. There is no need for ionizing radiation, it is small and portable, and the testing time is fast (about one minute).