Bone Density Test

Bone is living tissue. It is constantly being remodeled through continuous uptake of old bone and deposit of new bone. This keeps the bones healthy and repairs any minor damage. Osteoblasts are cells that lay down new bone and osteoclasts are cells that reabsorb old bone. When there is a mismatch between the osteoclast and osteoblast, it results in osteoporosis. It also occurs as a result of aging, changes in normal hormones, and diets low in calcium and vitamin D. 

A bone density test determines if you have osteoporosis, a condition that makes bones more fragile and thus more likely to break.

In the past, this condition could only be detected after a bone fracture occurred. By that time, however, your bones could already be weak.

A bone density test enhances the precision of calculating the risk of bones breaking.

This test makes use of X-rays to measure how many grams of calcium and other essential bone minerals are packed into one segment of bone. Bone density can be measured through different procedures, the majority of which are quick and painless. A popular technique that is fast and highly accurate is the dual energy X-ray absorptiometry (DEXA). It uses a special X-ray machine to measure bone density. Bone density test is also known as bone mass measurement.

The bones commonly tested are the spine, hip, and forearm.            

Many people have this test done every few years as they get older. This is to discover and treat osteoporosis and prevent fractures and other disabilities. Generally, women and men under the age of sixty-five do not need this test for the following reasons:

1. Most people do not have serious bone loss; people usually have mild bone loss called osteopenia. They do not need the test, because their risk of breaking a bone is low. Such people should exercise and get enough calcium and vitamin D in order to prevent greater bone loss.  
2. A bone density scan has risks. The scan emits a small amount of radiation. But this radiation exposure can add up and affect the body over one’s life, hence, it is best to avoid it if possible.

The bone density scan was invented by the late John R. Cameron. He was a professor at the University of Wisconsin at Madison. He invented bone densitometry, which uses very small, but precise radiation measurements to determine the mineral content of bone. It was one of the most important contributions to medical physics. 

Bone density testing is done for the following reasons:

• To identify a decrease in bone density before you actually break a bone
• To determine your risk of broken bones (fractures)
• To confirm a diagnosis of osteoporosis
• To monitor osteoporosis treatment

The higher the mineral content in a bone, the denser it is, and the denser the bone, the stronger it is and less likely to fracture.

A bone density test must not be mistaken for a bone scan. Bone scans require injections beforehand, and their purpose is to detect fractures, cancers, infections, and other peculiarities of bone. Although more common in older women, osteoporosis can also develop in men.

Osteoporosis is common in the elderly, especially females. Certain conditions, such as endocrine failure, chronic liver disease, and chronic liver failure, can contribute to bone loss.

Your doctor can recommend a bone density test if you have:

• Lost at least four centimeters from your height
• Fractured a bone
• Taken certain drugs, such as steroid medications, that interfere with the bone re-building process
• Received a transplant; people who have received a transplant, either organ or bone marrow, are at a higher risk of osteoporosis, partly because of the anti-rejection drugs that interfere with the bone re-building process.
• Had a drop in hormone levels; in addition to the natural drop in hormones that takes place after menopause, women's estrogen may also drop during certain cancer treatments.
• Low body weight or thin body stature
• Advanced age
• Impaired vision
• Estrogen deficiency at an early age
• Dementia
• Lifelong calcium intake
• Low physical activity
• Thyroid disease
• Excessive caffeine consumption
• Use of oral contraceptives

Some treatments for prostate cancer reduce testosterone levels in men. Lower sex hormone levels weaken bones.

Women aged sixty-five and men aged seventy should get a DEXA scan. They can talk to their doctors about the risks and benefits of one. If men and women aged fifty-nine to sixty-nine have risk factors for serious bone loss, they should consider this test. Risk factors include having rheumatoid arthritis, having a parent who broke a hip, smoking, heavy drinking, and having disorders associated with osteoporosis. Depending on the results of your first test, you may need a follow up bone-density test.

If a person has bone loss, the most common drugs given to treat it are Fosamax and Actonel. These drugs have benefits as well as risks, too. Common side effects include upset stomach, heart burn, and difficulty swallowing. Rare effects include bone, pain, and/or muscle pain, cracks in the thighbones, heart rhythm problems, and bone loss in the jaw. People may be given these drugs if they suffer from minor bone loss, but there has been little evidence that these drugs are helpful. 

Relationship Between BMD and Fracture Risk

If a patient has low bone mass at the hip or spine, it is measured with a DEXA. In such patients, there is a two-to three-fold increase in the incidence of osteoporotic fracture. In other words, a person who has low bone density at the measured area of spine and hip could be at an increased risk of future osteoporotic fractures at other parts besides the spine and hip. 

Undergoing a bone density test comes with potential risks.

The limits of bone density testing include:

• Differences in testing methods
• Central apparatuses, designed to measure the bone density of the spinal and hip bones, are more accurate, but more expensive compared to peripheral apparatuses, which measure the bone density of the forearm, finger, and heel bones.

Testing might not be covered by insurance. Therefore, it is advisable to ask your insurance provider beforehand if you are covered.

A bone density test can confirm you have low bone density, but it cannot give you the cause. To find that out, you have to complete a full medical evaluation.

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

If you are having your test done at a medical center or hospital, be sure to inform your doctor if you have recently had a barium exam or contrast material injected for a CT scan or nuclear medicine test, as contrast materials may interfere with your bone density test.

In most cases, bone density tests are done to bones that are more likely to break because of osteoporosis, including:

• Lower spine bones (lumbar vertebrae)
• The narrow neck of the thigh bone (femur)
• Bones in the forearm

If you have a bone density test at a hospital, it will probably be done using a central device, where you lie on a padded platform, while a mechanical arm passes over your body. You are exposed to a very small amount of radiation, and the test usually takes about ten to thirty minutes.

A small, portable machine can take a bone density measurement as far as the ends of your skeleton, such as those in your fingers, wrist, or heel.

The instruments used for these tests are called peripheral devices and are often found in pharmacies.

Because bone density can vary from one region of the body to another, a measurement taken at the heel is usually not as accurate a predictor of future fractures as one taken at the spine or hip. That is why, if the test on a peripheral device is positive, a follow-up scan may be recommended by the doctor at the spine or hip to confirm the diagnosis.

There are several procedures used to measure bone density, which include:

• Dual energy X-ray absorptiometry: This is one of the most common methods. It is fast and highly accurate. It uses different energy X-ray beams to detect bone and soft tissue density separately. It can measure bone density in the spine, forearm, and entire body as well.
• Single energy X-ray absorptiometry: In this, a single X-ray beam is used to measure bone density at peripheral sites like the forearm and heel. The area to be tested is wrapped in a tissue-like substance, then immersed in water; this improves the quality of the results.
• Ultrasound: With an ultrasound, the measurements obtained may provide data on the structural integrity of the bone. A quantitative ultrasound is a new ultrasound device that can estimate the bone density of the heel. It produces results in minutes and provides an automatic print-out of them. The ultrasound beam is directed at the analyzed area, and the waves that are scattered and absorbed assess bone density. However, the results are not as precise compared to other methods. This technique is new and research is still being conducted on it. If the ultrasound shows a low BMD result, the doctor might ask for a DEXA scan to confirm the results.
• Quantitative computed tomography: This is used to assess BMD. For this test, a standard CT scanner is used. The amount of radiation exposure is higher compared to a DEXA and the cost is also greater, hence, it is not used in general for clinical tests.

Information on a DEXA report:

DEXA reports vary depending on the facility performing the test. However, all reports include the following:

• Date and location of the test, the medical equipment used viz the manufacturer and the model of the densitometer
• The reason for the test
• Overall diagnosis based on the test
• Results for each site that was tested
• Bone density, which is reported as a T-score and a Z-score
• If any prior tests were performed at the same medical facility, the comparison of bone density is shown.
• Some reports show a calculated estimate of the risk of bone fracture based on the results of the scan.
• Some reports include a vertebral fracture assessment. It uses the DEXA to check if there is any bone in the spine that is already fractured.
• Notation regarding how long before a follow-up test is needed

Bone density results are always reported in two numbers, a T-score and a Z-score.

• T-score: T-score is your bone density compared to what is normally expected in a healthy young adult of your sex. Your T-score is the number of units, called standard deviations, your bone density is above or below the average.
• What your score means: -1 and above means your bone density is considered normal. Between -1 and -2.5 indicates a sign of osteopenia, a condition in which bone density is below normal and may lead to osteoporosis. -2.5 and below means your bone density indicates you likely have osteoporosis.
• Z-score: Z-score is the number of standard deviations above or below what is normally expected for someone of your age, sex, weight, and ethnic or racial origin.
• If your Z-score is -2 or lower, it may suggest something other than aging is causing abnormal bone loss. If your doctor can identify the underlying problem, the condition can often be treated and the bone loss slowed or stopped.

Long-Term Outlook

For people who have osteoporosis, they might have to repeat bone density tests to make sure the treatment is serving its purpose. Try to visit the same testing facility for all future tests so that the same machine is used. This will rule out any measurement differences between machines or facilities.

How to Keep Bones Strong

• Exercise: The best exercise is to make your bones carry the weight of your whole body. Do at least thirty minutes of weight-bearing exercise daily.

• Get enough calcium and vitamin D: At least 1200mg of calcium are needed each day. Eat foods rich in calcium; if required, take a calcium pill. If you are a woman in menopause, take vitamin D, at least 800 IU a day.

• Avoid smoking and limit alcohol: Go for a stop-smoking program if you are a smoker. Limit your drinking, for women, to one drink a day, and for a man, two drinks a day.

• Avoid certain drugs: Some drugs like proton pump inhibitors (which are used to treat heart burn), corticosteroids, and newer antidepressants can damage bones. If you take any of these drugs, such as ompeprazole, lansoprazole, and pantoprazole, ask the doctor if these medications are right for you.