© Sebastian Kaulitzki | Dreamstime.com
What is osteoporosis? Think of it this way: Healthy bones are in a state of continuous breakdown and rebuilding. This process, called remodeling, is performed by specialized cells called osteoclasts, which resorb (break down) old bone, and osteoblasts, which form new bone.
In young adults, remodeling happens in a balanced fashion that maintains bone density over time. But as we age, and particularly when women reach menopause and estrogen levels plummet, the process is no longer balanced—more bone is broken down, and bone building is unable to keep up. The result is reduced bone density, an increased risk of bone mineral density (BMD) test scores of osteoporosis -2.5 or osteoporosis -3 bone density test score—and brittle bones that are more prone to fracture.
How Your Bone Density Is Measured
The standard approach for measuring bone density is dual energy X-ray absorptiometry (DEXA, also written as DXA), which measures the density of bones in the spine, hip, and wrist, since these are the areas most likely to be affected by osteoporosis and by the osteoporotic fractures that can result from BMD scores in the range of osteoporosis -2.5 and or osteoporosis -3.
A DXA scan takes about 20 minutes and is painless. It is essentially an X-ray procedure that measures how many grams of calcium and other bone minerals are packed into a segment of bone (typically the spine, hip, or forearm, since these are the bones most likely to fracture due to osteoporosis). Bone mineral density is calculated on the basis of how much of the X-ray beam passes through the bone.
Other methods of measuring bone density include ultrasound and computed tomography (CT). However, the results from ultrasound may not be as precise as with DXA, while CT scans expose the body to more radiation than DXA.
Get a FREE Special Report from the editors of University Health News, Bone and Joint Conditions: Gout symptoms, osteoarthritis treatments, rheumatoid arthritis pain relief, and more.
Learn the best ways to relieve your arthritis and osteoporosis pain and gout symptoms.
A smaller type of bone scanner can be used to measure peripheral bone mineral density in the finger, wrist, or heel. These types of machines, often available in pharmacies, don’t provide an accurate a measure of bone density; still, if a peripheral test is positive, discuss with your doctor whether you should have a follow-up scan of your hip or spine.
How Your Bone Density Is Calculated
DXA results compare your bone density to that of a healthy 30-year-old adult and come back as what’s called a “T-score.” A range of -1 and above indicates normal bone density, and between -1 and -2.5 indicates low bone density, which is sometimes referred to as osteopenia. Osteoporosis -2.5 indicates that you do have you may be on the threshold of full osteoporosis, and if your score is osteoporosis -3, you have osteoporosis -3 there’s usually no question you are suffering from the condition. These results roughly reflect how much bone you’ve lost—for example, osteoporosis -2.5 equates to 25 percent bone density loss, and osteoporosis -3 equates to 30 percent bone density loss.
Do you need a bone density test? Your doctor can help you decide if and when you might need one. In general, this testing is recommended for women age 65 and older along with younger postmenopausal women who have further risk factors for osteoporosis. Additional risk factors include lower body weight (less than 154 pounds, which means you might start out with less bone mass), a family history of osteoporosis, and a previous fracture after age 50. Smoking and three or more alcoholic beverages daily also raise your risk.
Your doctor also may advise that you be screened for osteoporosis -2.5 or osteoporosis -3 if you have certain co-morbidities, such as an overactive thyroid, or a gastrointestinal condition that impedes the absorption of calcium (for example, Crohn’s disease). Some medications, including corticosteroids such as prednisone (Deltasone, Liquid Pred), some antidepressants, and proton pump inhibitors (PPIs), which are used to treat heartburn, also may weaken your bones.
The National Osteoporosis Foundation (NOF) also recommends bone density testing every one to two years for women taking osteoporosis medications. If you’ve recently started taking these meds, your doctor will likely refer you for a repeat DXA after one year to monitor how well the medication is working.
Originally published May 2016 and updated.