What Is a Bone Density Test?

A bone density test measures the amount of calcium and minerals in the bones to determine how likely they are to break (fracture). Also called a bone mineral density test (BMD), a dual-energy X-ray absorptiometry test (DEXA scan), or a peripheral screening test, a bone density scan checks the hips, spine, forearms, heel, or finger for signs of decreased bone mass.

A bone density test gives a value called a T-score that helps providers diagnose decreased bone mass (osteopenia) and weak, brittle bones that are at the highest risk of breaking (osteoporosis). A bone density test does not show arthritis.

This article will discuss why you might need a bone density test, how it is done, the risks of having a bone density scan, and what your results mean.

Purpose of a Bone Density Test

In the United States, 18.8% of females aged 50 or older have osteoporosis of the femur neck (hip) or lumbar spine (lower back). Only 4.2% of males have osteoporosis.

Decreased bone density and strength can lead to weakened bones that easily break. A bone density test helps screen, diagnose, and monitor the effects of conditions that put people at higher risk for fractures, including osteopenia and osteoporosis.

Factors that can put you at a higher risk for poor bone strength and reduced bone density include:

• Family history of osteoporosis
• Having diabetes or rheumatoid arthritis
• Early menopause
• Lack of physical activity
• Alcohol and tobacco use
• Taking certain medications (e.g., glucocorticosteroids)
• Having a body mass index (BMI) under 21
• Postmenopausal White females over the age of 50

The U.S Preventive Services Task Force recommends bone density screening for females over 65 or who have risk factors for osteoporosis.

Talk to your healthcare provider about getting a bone density test if you're at increased risk for poor bone health.

Does a Bone Density Test Show Arthritis?

A bone density test does not show arthritis. Arthritis is an inflammatory condition that affects the joints. The signs of arthritis include joint pain, stiffness, and warmth. Most people with decreased bone density do not have symptoms unless they have broken a bone.

Some people with arthritis may need a bone density test to look at how being on steroids has affected their bones. Additionally, people with rheumatoid arthritis (RA) are at a higher risk for developing osteoporosis from chronic inflammation and other complex mechanisms.

Diagnosing arthritis can be difficult because there are many variations of the disease. A provider can do a physical exam, family history, medical history, imaging, and blood work to diagnose arthritis.

Risks and Contraindications

A bone density test (such as a DEXA scan) is relatively safe. However, you will be exposed to low-dose radiation during the test. Two very low-dose X-ray beams pass through your body's tissue to determine how dense and strong your bones are.

Contraindications

Tell your healthcare provider and X-ray technologist if you're pregnant or could be pregnant, as low doses of radiation can harm a fetus.

You should also tell the technologist if you've recently had any tests that used barium or another contrast material. You might need to wait 14 days after having these tests before you can have a bone density test.

Before the Test

A bone density test is usually quick and painless. Here are ways to prepare for a bone density test.

Timing

The bone density test itself takes 10 to 30 minutes, depending on the type of machine and body area being scanned. You'll want to allow an additional 30 minutes to complete some paperwork before the test.

Location

The central DEXA scan is the most common bone density test device. The machine is found in hospitals, medical clinics, and outpatient imaging centers.

The central DEXA is located in a room with a large table. A scanning device (detector) hangs over the table and an X-ray generator is below the table.

The X-ray technologist will give you instructions before and during the test but they will leave the room to take the pictures.

What to Wear

You might be asked to put on a gown for the test. If not, you'll be able to stay in your regular clothes but it will help if you wear something loose and comfortable. Avoid wearing metal zippers, belts, or jewelry.

Food and Drink

You can eat normally on the day of your bone density test. Do not take calcium supplements for at least 24 hours before the test (including Tums for indigestion). You may go back to your regular diet immediately after the test.

Cost and Health Insurance

Before the bone density test, check with your health insurance about coverage and how much a co-pay will be.

The cost of a bone density test depends on your type of health insurance, lack of insurance, or the state in which you live.

Medicare and most commercial insurance companies cover the cost of the test if you meet certain criteria. The estimated national average cost of a bone density test is $125.

What to Bring

You must bring proof of identification and your health insurance card to the appointment. You will be able to drive yourself home after the test, so you don't need to bring someone with you.

During the Test

Pretest

Once you have checked in and completed the admission paperwork, you will be taken to an exam room. At this time, you might be asked to change into a gown. Your personal items will be put in a safe place (like a locker) while you are having the test.

Throughout the Test

During the test, you will lie on your back (supine) on the table. Your legs will rest, straight or bent, on a padded box.

The detector above will pass over your body, and the X-ray generator will go under you. The two images will be combined and sent to a computer.

You will need to lay very still. You might be asked to hold your breath for a few seconds to ensure a clear image. The test takes between 10-30 minutes, depending on the device used and the body area being scanned.

Post Test

When the test is over, you can change back into your regular clothing, gather your items, and go home.

After the Test

Side effects of a bone density test are rare. You may go back to your normal activities immediately.

In addition to the bone density test, your healthcare provider may want you to have bloodwork done to analyze your calcium and vitamin D levels.

Interpreting Results

A specially trained doctor called a radiologist will interpret the bone density test. The results will be available to your healthcare provider a few business days after the scan has been completed.

The results of your bone density test will have two scores: a T-score and a Z-score.

• T-scores compare your bone density to a healthy young person with normal bone mass
• Z-scores compare your bone health to that of people who are your age

The T-score is the most important of the two values. Here are the ranges:

• Normal bone density: -1 and above
• Low bone density osteopenia: Between -1 and -2.4
• Osteoporosis: -2.5 and lower

Follow-Up

Follow-up testing after a bone density scan depends on your results and risk factors.

For example, if you are at high risk for fractures, you may need a repeat bone density scan every two years. If you have a moderate risk, you might need repeat testing every 3–5 years. If you're at low risk, you might only need to be tested every 10-15 years.

Whenever you have your next scan, try to have it at the same place you had your first. This will help ensure it is accurate.

If you are at risk for decreased bone density, your provider might recommend lifestyle changes that can improve your bone health. For example, plan meals that are rich in calcium and vitamin D, make time to exercise daily, quit smoking and reduce your alcohol intake, and come up with a strategy to maintain a healthy weight.

Summary

A bone density test, such as a DEXA scan, measures how much calcium and minerals are in your bones. This information helps your provider determine if you are at is at risk for fractures.

A bone density test can help diagnose osteopenia and osteoporosis, which decrease bone density and strength, but does not show arthritis.

It is a painless procedure that takes place at a hospital, medical clinic, or outpatient imaging center. The test takes 10 to 30 minutes, and the results are available after a few business days.

In the results, you get a T-score based on how your bones compare to healthy bones. These results determine when you will need another bone density test.