Bone Density Test

What is a bone density test?

People undergo bone density tests to determine if they have osteoporosis or osteopenia. This condition is characterized by bones that are more fragile and could more easily break.

A bone density test uses X-rays that measure how many grams of calcium and other bone minerals are found in a segment of bone. The spine, hips, and forearms are the bones most commonly tested.

Results from the test are used to help your doctor make the best possible recommendations for protecting your bones in the future before a broken bone occurs.

Traditional X-rays are sometimes used, but a more accurate diagnosis can be achieved with dual-energy X-ray absorptiometry (abbreviated as DXA or DEXA scan) or a special CT scan that determines the bone density of the spine or hip.

A single X-ray can only show changes in bone density after about a 40% loss. However, a DXA test uses two X-ray beams instead of one and can show changes in bone density as small as 1%.

There are two types of DXA tests:

Central DXA/DEXA scan. This is a non-invasive test of the hip and spine. If it's not possible to test these two areas, the radius bone of the forearm is tested instead. The hip and the spine are normally tested because they have the highest chance of breaking if you have osteoporosis.

Also, when either breaks, it can result in longer recovery times, more pain, and possibly even permanent disability ¹. A DXA test is the most popular and reliable bone density test.

Peripheral/Screening tests. These screening tests measure bone density in the lower arm, wrist, finger, or the heel.

There are different kinds of peripheral tests ².

• pDXA (peripheral DXA test) measures the heel or the wrist.
• SXA (single-energy X-ray absorptiometry) also measures the heel or wrist.
• QUS (quantitative ultrasound) sound waves measure density, usually at the heel.
• pQCT (peripheral quantitative computed tomography) measures density in the wrist.
• RA (radiographic absorptiometry) is an X-ray of the hand.

Bone density tests are different from bone scans. Bone scans require a pre-test injection beforehand and are used to detect fractures, cancer, infections, and other bone abnormalities.

A quick overview of osteoporosis

It’s estimated that about 10 million Americans suffer from osteoporosis. Another 44 million people have low bone density, which puts them at an increased risk ³.

Half of all women and up a quarter of all men will break a bone in their lifetime due to osteoporosis.

Osteoporosis is often referred to as a “silent disease.” That is because you can’t feel your bones growing weaker, and you may not even know you have osteoporosis until after you break a bone.

Osteoporosis is responsible for about two million broken bones annually. By 2025, that figure is estimated to rise to three million broken bones each year. This will cost Americans more than $25 billion.

Those who suffer from osteoporosis can break a bone due to a minor fall. In more severe cases, some people have been known to break a bone after bumping into furniture or a wall, or even something as simple and harmless as sneezing. 

Hip fractures are prevalent with osteoporosis. Sadly, about 24% of hip fracture patients over 50 die the following year. One quarter ends up in nursing homes and never regain full hip functions.

Exercising regularly and eating a proper diet (including the recommended amount of calcium and vitamin D) can slow or stop the loss of bone mass.

Why is bone density testing important? 

In addition to diagnosing and predicting osteoporosis, there are several upsides to a bone density test:

It's a simple and non-invasive procedure that requires no anesthesia.

The amount of radiation required for a DXA test is less than one-tenth of the dose of a standard chest X-ray.

A DXA test is the best standardized method available to diagnose osteoporosis and fracture risks.

Testing equipment is widely available so that having a test is convenient for patients and doctors.

Testing determines the level of bone health, which can then be used to determine the best course of treatment if it is required. Testing also allows your doctor to monitor the effects of the treatment prescribed for you.

A test lets you know if you have developed osteoporosis after you have broken a bone. 

Who should have a bone density test? 

Bone density testing may be recommended in several situations:

• You are a woman 65 or older.
• You are a man 70 or older.
• You have lost at least 1.5 inches in total height, which may be due to compression fractures in your spine caused by osteoporosis.
• You have a height loss of half an inch or more in one year
• You are a post-menopausal woman and are not taking estrogen.
• You have a personal/maternal history of hip fracture or smoking.
• You are a post-menopausal woman who is over 5 feet 7 inches or less than 125 pounds.
• You are a man with rheumatoid arthritis, chronic kidney or liver disease, or other clinical conditions that result in bone loss.
• You have received an organ or bone marrow transplant because anti-rejection drugs also interfere with bone-rebuilding.
• You have had a drop in hormone levels. Lower sex hormones weaken bones. This happens after menopause or in some cancer treatments.
• You use medications that cause bone loss. These include corticosteroids (Prednisone), anti-seizure medications (Dilantin and some barbiturates), or high-dose thyroid replacement drugs.
• You have type 1 diabetes, liver disease, kidney disease, or a family history of osteoporosis.
• You have high bone turnover, diagnosed by excessive collagen in urine samples.
• You have a thyroid condition (i.e., hyperthyroidism).
• You have a parathyroid condition (i.e., hyperparathyroidism).
• You experienced a bone fracture after only mild trauma. 

You may also be referred for a bone density test if you are diagnosed, or it is suspected that you have Paget's disease.

This is a chronic condition that interferes with your body’s bone remodeling process. Bone remodeling occurs when new bone tissue gradually replaces old bone tissue.

It usually occurs in the pelvis, spine, legs, and skull and can result in broken bones, hearing loss, and pinched spinal nerves.

Researchers believe genetics and environmental factors cause Paget's disease. Several mutated genes are linked to the disease. Some scientists also believe that Paget's may be caused due to a measles virus infection in your bone cells. But this theory has not been proven.

There are two types of Paget’s disease. When a single bone site is affected, it is referred to as monostotic Paget's disease. When multiple bones are affected, it is referred to as polyostotic Paget’s disease.

How a bone density test is done 

The test is usually performed on an outpatient basis. It is painless and takes about 15 to 30 minutes.

In a central DXA test, the patient lies on a padded table. An X-ray generator is below the patient, and an imaging device is above. When activated, the DXA machine sends a thin and invisible beam of low dose X-rays.

Two energy peaks are used. One is absorbed by soft tissue, and the other is absorbed by bone. The soft tissue amount is subtracted from the total amount and software computes and displays the remaining amount, which is your bone density measurement.

The peripheral tests only require the placement of a finger, hand, forearm, or foot in a small device that generates a bone density reading in a few minutes.

How to Prepare for a Bone Density Test 

Preparation for a bone density test is fairly simple.

On the day of your test, you can eat normally. The only exception is that you should not take calcium supplements for at least 24 hours before the test.

Wear loose and comfortable clothing. Avoid items with metal zippers, buttons, or belts. Be sure to take your keys, money clips, loose change, or a wallet out of your pocket if they are in the area to be scanned.

You will be asked to remove jewelry, dental appliances, eyeglasses, or any other metal objects that could interfere with the X-rays.

You will also be asked to wear a gown instead of some of your clothes while the test takes place.

 Women need to let their doctor and X-ray technician if they think they are pregnant. Most tests are not performed during pregnancy to avoid exposing a fetus to radiation.

Also, be sure to let your doctor know if you have had a barium exam or had any contrast material injected as part of a nuclear medicine test or CT scan within the previous two weeks ⁴.

What to expect from bone density test results

Bone density test results are reported in two ways: your T-score and your Z-score.

Your T-score is a comparison between you and what is normal in a healthy 30-year-old adult of your particular sex. T-scores are reported in what is called "standard deviations."

A T-score of -1 and above means your bone density is normal.

A T-score of between -1 and -2.5 indicates a sign of osteopenia. This means your bone density is below normal and could be a precursor of osteoporosis.

A T-score of -2.5 or more means that you likely have osteoporosis.

Your Z-score is reported as the number of standard deviations above or below what is normal for someone of your body size, sex, weight, age, and ethnic origin. If your Z-score is much lower than average, it may be due to something other than aging that could be the cause of abnormal bone loss.

Risks and limitations of bone density testing 

Because a bone density test is non-invasive and takes less than 15 minutes, you are exposed to very little radiation.

However, the exposure is there, and so, there is always a minimal risk of developing cancer from excessive exposure. Modern x-ray systems low dose controls and have very controlled beams to prevent scatter radiation.

A few central DXA machines can measure bone density in the hip and spine of people who weigh up to 400 pounds. But most machines are limited to people who weigh 300 pounds or less. In these cases, healthcare providers will perform a central DXA test of the radius bone in the forearm and a peripheral bone density test of a heel bone.

If you repeat a bone density test, try to use the same testing equipment each time. This is the best way to ensure accuracy when compared to your previous result. When this isn’t possible, you still need to work with your doctor to compare both bone density scores to see what changes have taken place.

You should know that the results from a central DXA test can't be compared to the results of a peripheral test.

Another limitation is that not all health insurance providers pay for bone density tests. Be sure to check with your insurer before committing to a test, so you know where you stand financially with out-of-pocket expenses. 

Also, while a bone density test can confirm you have low density, the test can’t tell you the cause. You will need to undergo additional testing to determine the cause and an appropriate course of treatment. 

Screening tests are merely an indication that you might benefit from more accurate and detailed bone density testing. These types of tests are usually found at health fairs, medical offices, and other public gatherings. These types of screenings should only be used as a general indicator of osteoporosis and not as a final word.

Women need to take extra precautions if they think they are pregnant.

The effectiveness of a DXA test is of limited if you have a spinal deformity or you’ve had spinal surgery. If you have a vertebral compression fraction or osteoarthritis, a CT scan will produce a more accurate response. 

How often should you have a bone density test? What is the cost of a bone density test?

If you’re already taking osteoporosis medication, many doctors and the National Osteoporosis Foundation recommend a bone density test every one to two years ⁵.

If you’re starting a new osteoporosis medication, then doctors will prescribe a bone density test after one year. There is some disagreement on frequency. For example, the American Medical Association recommends testing after the first three years of a new treatment because bone density changes slowly over time. 

Many health insurance companies provide coverage for a bone density test. But there may be restrictions or limitations. For example, some insurers will only pay for the test if you’ve broken a bone, been through menopause, or you’re taking medications that cause your bones to thin. Coverage may also be provided if you’re not taking estrogen at menopause ⁶.

Medicare also pays for bone density testing once every two years for people 65 and older in some situations. These include:

• Women diagnosed with low estrogen and at risk for osteoporosis
• People whose X-rays indicate they may have osteoporosis, osteopenia, or spine fractures
• People who take steroid medications or those who will be taking them soon
• Patients with primary hyperparathyroidism
• Those being monitored to gauge if their osteoporosis drugs are effective or not

You should check with your healthcare provider to see what your coverage is for a bone density test and what your out-of-pocket expenses are to avoid any unpleasant financial surprises after the fact. 

Treatment and Outlook

Depending on the results of your test, your doctor may make treatment recommendations to reduce your chances of breaking a bone.

Before doing so, your current health situation will be evaluated, including your risk of breaking a bone, as well as your current health and your medical history.

For men 50 and older and post-menopausal women, suggested treatment guidelines are as follows ⁷:

• If your T-scores are -1.0 and above (normal bone density), you do not need to take an osteoporosis medicine.
• If your T-scores are between -1.0 and -2.5 (low bone density or osteopenia), you may want to consider taking an osteoporosis medicine depending on your individual risk factors.
• If your T-scores are -2.5 and below, you should consider taking osteoporosis medicine.

Several possible osteoporosis drugs can be prescribed. Which one you take will depend on your personal factors. Doctors will consider your age, menopausal status, current bone density, family history, and other potential risk factors. Some drugs also produce side effects, and this will need to be considered, as well.

Diet

You should also eat properly to minimize the effects of osteoporosis. Make sure you’re getting your recommended daily amounts of calcium by consuming:

• Dairy products, such as low-fat and non-fat milk, cheese, and yogurt.
• Fish, including canned sardines and salmon, mackerel, and tuna.
• Meat and other high protein foods (in moderation)
• Fruits and vegetables rich in vitamin D, such as collard greens, turnip greens, okra, kale, broccoli, spinach, beet greens, artichokes, potatoes, soybeans, brussels sprouts, plantains, sweet potatoes, and raisins. Other good sources of nutrients include tomato products, red and green peppers, oranges, blueberries, grapefruits, strawberries, bananas, and prunes.
• Fortified foods with added calcium and vitamin D, such as cereals, breads, juices, soy milk, and others.

And, believe it or not, some studies have also shown that some alcoholic and non-alcoholic beverages like wine, beer, and tea in moderation may also be good for your bones ⁸.

Limit alcohol to 2 - 3 drinks per day; otherwise, heavy drinking could contribute to bone loss.

Also, try to limit yourself to no more than three cups of coffee a day because caffeine does decrease calcium absorption.

Consider supplementing your current diet by taking multivitamins or supplements.

Exercise

There are several strength and mobility exercises you can do that also promote bone health.

Talk to your doctor or a physical therapist about posture and balance exercises as well as those that specifically strengthen the hips and spine.

You may also be directed to perform functional exercises that target specific activities such as getting up from a chair or going up and down stairs.

Outlook

Overall, the outlook for people with osteoporosis is good, especially when it is diagnosed and treated early. In most cases, the condition can be stabilized or improved, substantially reducing the risk of fractures.

For more information

The leading advocacy group for osteoporosis is the National Osteoporosis Foundation (NOF).

Visit their website or contact them directly here.