Bone density test

A bone density test determines if you have osteoporosis — a disease that causes bones to become more fragile and more likely to break.

In the past, osteoporosis could be detected only after you broke a bone. By that time, however, your bones could be quite weak. A bone density test enhances the accuracy of calculating your risk of breaking bones.

A bone density test uses X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone. The bones that are most commonly tested are in the spine, hip and forearm.


Why it's done Risks How you prepare What you can expect Results

Doctors use bone density testing to:

  • Identify decreases in bone density before you break a bone
  • Determine your risk of broken bones (fractures)
  • Confirm a diagnosis of osteoporosis
  • Monitor osteoporosis treatment

The higher your bone mineral content, the denser your bones are. And the denser your bones, the stronger they generally are and the less likely they are to break.

Bone density tests differ from bone scans. Bone scans require an injection beforehand and are usually used to detect fractures, cancer, infections and other abnormalities in the bone.

Although osteoporosis is more common in older women, men also can develop the condition. Regardless of your sex or age, your doctor may recommend a bone density test if you've:

  • Lost height. People who have lost at least 1.6 inches (4 centimeters) in height may have compression fractures in their spines, for which osteoporosis is one of the main causes.
  • Fractured a bone. Fragility fractures occur when a bone becomes so fragile that it breaks much more easily than expected. Fragility fractures can sometimes be caused by a strong cough or sneeze.
  • Taken certain drugs. Long-term use of steroid medications, such as prednisone, interferes with the bone-rebuilding process — which can lead to osteoporosis.
  • Received a transplant. People who have received an organ or bone marrow transplant are at higher risk of osteoporosis, partly because anti-rejection drugs also interfere with the bone-rebuilding process.
  • Had a drop in hormone levels. In addition to the natural drop in hormones that occurs after menopause, women's estrogen may also drop during certain cancer treatments. Some treatments for prostate cancer reduce testosterone levels in men. Lowered sex hormone levels weaken bone.

Limitations of bone density testing include:

  • Differences in testing methods. Central devices, which measure the density of your spinal and hip bones, are more accurate, but cost significantly more than do peripheral devices, which measure density in the forearm, finger or heel bone.
  • Might not be covered by insurance. Not all health insurance plans pay for bone density tests, so ask your insurance provider beforehand if you're covered.
  • Doesn't identify the cause. A bone density test can confirm that you have low bone density, but it can't tell you why. To answer that question, you need a more complete medical evaluation.

Bone density tests are easy, fast and painless. Virtually no preparation is needed. In fact, some simple versions of bone density tests can be done at your local pharmacy or drugstore.

If you're having the test done at a medical center or hospital, be sure to tell your doctor beforehand if you've recently had a barium exam or contrast material injected for a CT scan or nuclear medicine test. Contrast materials might interfere with your bone density test.

Bone density tests are usually done on bones that are most likely to break because of osteoporosis, including:

  • Lower spine bones (lumbar vertebrae)
  • The narrow neck of your thighbone (femur), next to your hip joint
  • Bones in your forearm

If you have your bone density test done at a hospital, it'll probably be done on a central device, where you lie on a padded platform while a mechanical arm passes over your body. The amount of radiation you're exposed to is very low, much less than the amount emitted during a chest X-ray. The test usually takes about 10 to 30 minutes.

A small, portable machine can measure bone density in the bones at the far ends of your skeleton, such as those in your finger, wrist or heel. The instruments used for these tests are called peripheral devices, and are often found in pharmacies. Tests of peripheral bone density are considerably less expensive than are tests done on central devices.

Because bone density can vary from one location in your body to another, a measurement taken at your heel usually isn't as accurate a predictor of fracture risk as is a measurement taken at your spine or hip. That's why, if your test on a peripheral device is positive, your doctor might recommend a follow-up scan at your spine or hip to confirm your diagnosis.

The doctor will discuss the report with the patient in detail. If the results are normal then the patient is fit and healthy with adequate bone strength as required. But, if the report shows abnormal levels of bone loss, then the doctor might advise the patient to undergo some additional tests to get a clear picture of the cause of the bone density problem, as the bone density test can only check the amount of bone mass loss and not detect or tell a specific reason for the problem. The results received after the bone density test will be available in the format as mentioned below:

 

  • T-score – This provides a comparison between the patient’s bone density and that of a healthy person of similar age and gender. This score is measured in the unit of standard deviation. T-score helps in measuring if the bone density of the patient is normal, below normal or above the normal levels.

 

 

T-score

T-score meaning

-1 and above

Bone density is normal

Between -1 and -2.5

This is a sign of osteopenia, which means that the density of bone is below normal level and may further lead to osteoporosis.

-2.5 and lower

Bone density test indicates that the patient is suffering from Osteoporosis

 

 

Z- score – This score helps to compare the loss of bone mass to that of the healthy people of the same age, sex, and size. If a patient has a Z-score below -2.0, it means that the patient has comparatively less bone density than that of an individual of the same gender, size, and age. The less bone density may not be due to aging but because of some disease condition. If the doctor detects the exact reason for the cause of bone density loss then it is easier to start a proper treatment on time and hence, decrease or control the further bone loss in the patient.

 

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