The single best predictor of bone strength is bone density. Bone density cannot be determined from plain X-rays, but a specialized low-dose X-ray technique called bone densitometry can be used to measure the amount of bone present in different parts of the skeleton. Research over the past decade has shown conclusively that bone density is related to risk of fracture, in much the same way that blood cholesterol is related to the risk of heart disease. The lower the bone density, the greater the risk of fractures due to osteoporosis.

Take our quiz to find out if you are a good candidate for a bone density test. If you answer "yes" to one or more of these questions, talk to your doctor about getting a bone density test.

Types of Bone Density Tests

We offer a variety of techniques to diagnose osteoporosis by determining the density of your bones. Expert consultation is available to assist in ordering the appropriate diagnostic examination. The different scanning techniques are:

Dual X-ray absorptiometry (DXA) of the lower (lumbar) spine and hip. This is the most common way to measure bone density. The DXA uses fan beam technology allowing for rapid scanning with very low-energy X-rays. The spine and hip exams each take about five minutes. DXA of the forearm also may be helpful, especially if both hips have been replaced surgically. The Hologic Delphi scanner at Mount Zion also can perform a low-dose X-ray to evaluate for spinal fractures. DXA tests are painless. You will be asked to change into a hospital gown to prevent any clothing or metal objects from interfering with the test. You will lie on a table and the scanning arm is moved slowly over the parts of the body to be scanned. You are not in a tunnel as with an MRI. The test takes about 10 to 15 minutes.

Ultrasound of the heel. Bone density of the heel predicts overall fracture risk. However, ultrasound of the heel is not as good at predicting hip and vertebral fractures as DXA of the hip and spine. There are some instances in which your doctor might select this exam instead of, or in addition to, a DXA.

Other bone related examinations also may be helpful, depending on your particular circumstances:

Quantitative computerized tomography (QCT) of the lower (lumbar) spine. This exam uses a standard CT scanner. Two vertebrae in the lower back are selected for single cross-sectional scans, which are analyzed with special densitometry software. The entire procedure takes about 15 minutes. This exam sometimes is used if you have a lot of arthritis in your back, which makes the DXA test less reliable. This exam isn't always covered by insurance and isn't covered by Medicare.

Lateral radiographs of the thoracic and lumbar spine. Using a conventional X-ray unit, views of the upper and lower spine are taken to see if you have any fractures. This is a 15-minute exam.

The recommended clinical examination consists of DXA of the spine and hip. QCT and lateral radiographs of the spine may be needed depending on the DXA results and your particular circumstances.

Reviewed by health care specialists at UCSF Medical Center.

Related Information

UCSF Clinics & Centers


Endocrinology Clinic at Mount Zion
2200 Post St., Suite C-432
San Francisco, CA 94115
Phone: (415) 885–7574
Fax: (415) 885–7724
Appointment information

Endocrinology Clinic at Parnassus
400 Parnassus Ave., Suite A-550
San Francisco, CA 94143
Phone: (415) 353–2350
Fax: (415) 353–2337
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Rheumatology Clinic
400 Parnassus Ave., Floor B1
San Francisco, CA 94143
Phone: (415) 353-2497
Fax: (415) 353-2530
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Skeletal Health Service
1500 Owens Street, Suite 430
San Francisco, CA 94158
Phone: (415) 353-2808
Fax: (415) 885-3862
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