How osteoporosis is diagnosed

A bone density test can help you determine if you have osteoporosis or are at risk.

How do you know if you have osteoporosis or if you are at risk? This is a common question, and one to get answered sooner rather than later.

Because bone loss typically happens gradually and painlessly, the first sign of osteoporosis can be breaking a bone, often more easily than you'd expect. But it is possible to determine if you have osteoporosis, even before a bone is broken, by getting a bone density test. The test can also detect if your bone density is lower than normal for a person of your age and sex. Bone loss that has not reached the stage of an osteoporosis diagnosis is called osteopenia.

Bone density testing

A bone density test is as close as your doctor can come to predicting your future bone health. The test results will show if you have osteopenia or osteoporosis, and how susceptible your bones are to fracture. A bone density test is the best way to predict fracture risk.

The test uses X-rays to measure how many grams of calcium and other bone minerals are in a square centimeter of bone. Generally, the higher the mineral content, the denser the bone is. And the denser bones are, the less likely they are to fracture.

Bone density testing uses a device called a bone densitometer. Most densitometers measure how much of a low-energy X-ray beam is absorbed as it passes through bone, in comparison to the absorption as the beam passes through the soft tissues next to the bone. The amount of X-ray energy that enters the bone is also compared with the amount of energy that leaves the bone. Denser bone absorbs more of the X-ray beam.

Central densitometers

These machines, typically found in hospitals and medical centers, are used to measure the density of the central, stabilizing parts of the skeleton, such as the spine and hip. This type of densitometer provides the most accurate bone density testing and can predict your potential risk of fracture.

Dual energy X-ray absorptiometry (DXA). A DXA machine uses two different X-ray beams to increase the precision of what it's measuring. As you lie on a padded platform, two mechanical arms containing an X-ray source and detector above and below your body are aligned. DXA is most often performed on the narrow neck of the upper leg bone (femur), just below the hip joint, as well as the lumbar vertebrae, which form the lower part of the spine. DXA testing is painless and takes only a few minutes.

Quantitative computerized tomography (QCT). This instrument measures bone density using computerized tomography (CT). Similar to having a CT scan, you lie on a movable padded table that slides into a large cylinder, where X-ray images are obtained from all angles. QCT is most often used to measure density in the vertebrae and the part of the femur below the hip.

Peripheral densitometers

Smaller devices are used to measure bone density on the periphery of the skeleton, such as in the wrist and heel bone. Although they are more portable, these densitometers are less accurate at predicting fracture risk. If your test on a peripheral device is positive for osteopenia or osteoporosis, then your doctor might recommend a follow-up scan of your spine or hip to confirm the diagnosis.

Quantitative ultrasound (QUS). This procedure is often called heel ultrasound because it typically measures bone density in the heel bone. Instead of X-ray radiation, QUS sends high-frequency sound waves through your heel while you rest your bare foot on the instrument. This type of densitometer measures the reflection of sound waves. Denser bone reflects sound waves back to the device sooner.

Peripheral dual energy X-ray absorptiometry (pDXA). This device is a compact, portable DXA scanner. Using X-rays, pDXA measures bone density in the wrist or heel. Although it's quick and accurate, this testing can be expensive.

Peripheral quantitative computerized tomography (pQCT). This portable version of QCT measures the bone density of the wrist or hand. This test is also expensive, and it produces a higher radiation exposure than do other tests.

Other types of testing, including 3-D imaging and high-resolution magnetic resonance imaging (MRI), are also under investigation.

March 10, 2017