What do bone density test results mean?

What is a bone density test? | Causes and risk factors | Bone density test preparation | Prices | Bone density test results | Osteopenia vs. osteoporosis | Treatment

Having strong bones is important to your health. They help you move and protect your internal organs from injury. Aging and certain medical conditions can weaken bones, resulting in low bone mass or low bone density. Bone density, or bone mineral density, refers to the amount of calcium and other minerals in your bone per volume measurement. “The higher your bone mineral density is, the stronger your bones are,” says Ellen Johnson MD, a board-certified radiologist in North Andover, Massachusetts. “Lower bone mineral density increases your risk of fracture.”

It’s possible to have weak bones without even knowing it. People often don’t have any symptoms until they break a bone. To prevent this, your healthcare provider may order a bone density test, or bone density scan, if you meet certain criteria. 

What is a bone density test?

Bone density is most commonly measured by a test called a DEXA scan (also called a DXA test), which uses X-rays to measure the amount of bone mineral, most commonly in your hips and lower spine. A DEXA scan is a quick and painless procedure that is very accurate at detecting bone loss. “Unlike ordinary X-rays, DEXA scans can measure tiny losses in bone density. This makes it possible to catch osteoporosis in its early stages,” Dr. Johnson says. 

“Other [preliminary] methods to measure bone density include ultrasound, quantitative computed tomography (QCT), and peripheral dual-energy X-ray absorptiometry (pDEXA),” explains Gethin Williams, MD, Ph.D., a medical director at Imaging and Interventional Specialists in El Paso, Texas. Portable machines, called peripheral devices, can measure bone density at your finger, wrist, or heel—but they usually aren’t as accurate as medical tests taken at the spine or hip. Any findings from these tests should be confirmed with a DEXA scan.

The National Osteoporosis Foundation recommends testing on the following schedule:

• Women age 65 and older
• Men age 70 and older
• Men and women older than 50 who have broken a bone recently

Your provider may also order a bone density measurement if you have reached a certain age and have risk factors for osteoporosis. Other national organizations have published different guidelines on osteoporosis screening. For instance, the United State Preventive Task Force Service guideline states that there is insufficient evidence to recommend osteoporosis screening in men. 

What causes low bone density?

As you grow, your bones are constantly breaking down old bone and generating new bone material. Most people reach their peak bone mass by age 30 after which, your body stops making new bone at the same rate it’s broken down. Meaning, bone mass decreases more quickly than it is replaced. 

Risk factors for osteoporosis

When your bone density gets too low, you’re at risk for osteoporosis. Your risk depends on many different factors—some of which are not in your control and some which can be helped with lifestyle changes.

There are several risk factors for developing osteoporosis including:

• Family history of osteoporosis
• Sex, women are more likely to develop osteoporosis especially after menopause
• Race, people who are white or of Asian descent have higher risk
• Age, your risk increases as you get older
• Size, people with smaller frames have higher risk because they have less bone mass to begin with
• Smoking tobacco
• Excessive alcohol consumption 
• Very low body weight due to an eating disorder
• Sedentary lifestyle
• Certain medical conditions, such as gastrointestinal diseases that affect nutrient absorption, cancer, multiple myeloma, rheumatoid arthritis, or kidney disease
• Certain long-term medication use, especially steroids like prednisone
• Change in hormone levels

In men, a drop in testosterone can decrease bone density; this can occur during prostate cancer treatment. In women, a drop in estrogen can lead to bone loss; this may occur for postmenopausal women or with certain cancer treatments.

In general, anything that causes chronic inflammation—including infection—can lead to decreased bone density because of the continuous production of pro-inflammatory cytokines. “Cytokines are small molecules that help regulate the immune system,” Dr. Williams says. “Normal bone metabolism involves a balance of bone destruction and formation called bone turnover. Since cytokines promote osteoclasts (cells that destroy bone) and inhibit osteoblasts (cells that build bone), the normally balanced bone turnover is abnormally unbalanced, promoting bone destruction.” This leads to abnormally decreased bone density.

How to prepare for a bone density scan

A DEXA scan is a quick, painless procedure, usually lasting only five to 10 minutes. The following steps can make it go even more smoothly.

• Wear loose, comfortable clothing, without metal zippers, belts, or buttons. These may obscure your hip or spine during the test. 
• Stop taking calcium supplements at least 24 hours before the test. They may artificially elevate your score.
• Discuss special health concerns with your provider. For example, if you’re pregnant or breastfeeding or recently had other scans or tests, you may need to delay your bone density scan. “Contrast material used in radiology or materials used in nuclear medicine may interfere with your bone density scan,” Dr. Williams says.

How much does a bone density test cost?

Without insurance, a DEXA scan can cost $125. However, as a preventative screening, bone density tests are typically covered by insurance for at-risk patients, according to American Bone Health. Medicare Part B also covers bone density tests every 24 months as long as you meet certain conditions.

Bone density test results

DEXA scan results include a T-score and a Z-score. They are calculated by how many standard deviations (SD) your test is from the reference point. 

• T-score: The difference between your bone mineral density (BMD) and a healthy young adult (30-year-old). Used to diagnose osteoporosis related to aging.
• Z-score: The difference between your BMD and someone of your age, race, height, and weight. Used to diagnose secondary osteoporosis (caused by another medical condition) or osteoporosis in children, teens, premenopausal women, and men younger than 50.

The two scores are calculated the same way, just compared to different groups. 

Osteopenia vs. osteoporosis

Osteopenia and osteoporosis are two disorders of low bone mineral density, says Rajnish Jaiswal, MD, associate chief of emergency medicine at NYC Health and Hospitals Metropolitan Hospital in New York. With both conditions, your bone mass is lower than usual for your age, but osteopenia is less severe. 

Osteopenia is low bone density (T-score between -1 and -2.5 SD). Osteopenia is the middle ground between a normal bone density and osteoporosis. “As we age, osteopenia is a natural process, but if it progresses to osteoporosis, the bones can become so thin and weak that a minor fall or even everyday activities can cause a fracture,” Dr. Williams says. With medical advice and lifestyle modifications, like diet and exercise, it can frequently be prevented from progressing to osteoporosis. The CDC shows that 43% of adults 50 and older have osteopenia.

The diagnosis of osteoporosis is based on a T-score equal to or lower than -2.5 SD. Bones have a thick cortex, or strong outer layer, surrounding a central area that looks like a kitchen sponge. “With osteoporosis, the normal little porous holes become much more prominent,” explains Dr. Johnson. “The central ‘sponge’ bone becomes much less dense, so the bones lose strength and are more easily broken.” In the United States, about 14.1 million adults 50 and older (or 13% of the age group) have osteoporosis, according to the CDC.

Both osteopenia and osteoporosis can cause broken bones or hip fracture, says Dr. Williams. “The prognosis for osteopenia is generally good, provided that the condition is diagnosed and treated early. However, the prognosis for osteoporosis is generally poorer, as the bones have already begun to thin and weaken,” Dr. Williams says.

How to increase bone density

Low bone density levels can be treated either with lifestyle changes or with medications depending on the severity. “If your T-score is under -2, you need to be sure you are doing regular weight-bearing exercise and you are getting enough vitamin D, with supplements if necessary, and dietary calcium,” says Dr. Johnson. “If you’re closer to -2.5, your doctor may consider adding medication to keep your bones healthy.”

Lifestyle changes

There are many things you can do to maintain or improve your bone health, including:

• Increasing calcium and vitamin D intake via diet or supplementation if needed to reach recommended daily intake values 
• Exercising regularly, including weight-bearing exercises and strength training
• Avoiding smoking 
• Limiting alcohol consumption

It’s also a good idea to schedule regular checkups and DEXA scans to monitor your bone density.

Medications

According to Dr. Jaiswal, the following pharmacological treatments may be prescribed based on your fracture risk, BMD, and clinical risk factors: 

• Bisphosphonates such as Fosamax (alendronate), Actonel (risedronate), or Reclast (zoledronic acid)
• Prolia (denosumab), an injectable medication for bone loss
• Injectable bone-building drugs for severe osteoporosis such as Forteo (teriparatide), Tymlos (abaloparatide) and Evenity (romosozumab) 

Your provider may advise you to avoid certain medications that are known to decrease BMD, such as glucocorticoids, heparin, anti-seizure medications, and aromatase inhibitors, Dr. Jaiswal says. 

The bottom line? Getting enough dietary calcium, vitamin D, and weight-bearing exercise can prevent or control osteoporosis. If medications are needed, there are several options.