A bone density test is a quick, painless scan that measures how strong your bones are. The most common version, called a DEXA scan (dual-energy X-ray absorptiometry), takes about 15 to 20 minutes, uses a very small amount of radiation, and requires almost no preparation. Here’s what the experience looks like from start to finish.
How the Scan Works
A DEXA scan uses two X-ray beams at different energy levels. Bone and soft tissue absorb these beams differently, and the machine uses that difference to calculate exactly how dense your bones are. The scanner focuses on your lower spine and hips, since these are the areas most vulnerable to osteoporosis-related fractures. In some cases, the forearm is also measured.
The technology is precise enough to detect small changes in bone density over time, which is why it’s also used to monitor whether treatment for bone loss is working.
What Happens During the Test
You lie on your back on a padded table. In most cases, you can keep your clothes on, though you’ll want to avoid wearing anything with metal zippers, buttons, or underwire that could interfere with the images. You’ll also need to remove any jewelry near the scan area.
A scanning arm passes slowly over your hips and spine while a second scanner passes beneath the table. You need to stay very still during this process, and you may be asked to hold your breath briefly to prevent the images from blurring. Your legs will either be straight or resting on a padded platform, depending on which area is being scanned. The whole appointment typically lasts 15 to 20 minutes, and there’s no recovery time. You walk in, lie down, and walk out.
How to Prepare
Preparation is minimal, but there are a few things that can throw off your results. Stop taking calcium supplements at least 24 hours before the scan. Undigested calcium tablets can sit in your bowel and overlap with the image of your spine, artificially inflating your bone density reading.
If you’ve recently had a barium study, a CT scan with contrast dye, or a nuclear medicine test, let your doctor know before scheduling. Residual barium or contrast material in your digestive tract can also distort the results. In most cases, you’ll simply need to wait until those substances have fully cleared your system before getting an accurate DEXA scan.
Radiation Exposure
A DEXA scan delivers about 0.001 millisieverts of radiation. To put that in perspective, a standard chest X-ray delivers roughly 100 times more (0.1 millisieverts). The dose from a bone density scan is roughly equivalent to the background radiation you absorb in about three hours of normal daily life. It’s one of the lowest-radiation imaging tests available.
Understanding Your T-Score
Your results come back as a number called a T-score, which compares your bone density to that of a healthy 30-year-old adult at peak bone mass. The scale works like this:
- T-score of -1.0 or higher: normal, healthy bone density.
- T-score between -1.0 and -2.5: osteopenia, meaning bone density is lower than normal but not yet in the osteoporosis range. This is a signal that bone loss has started and preventive steps may help.
- T-score of -2.5 or lower: osteoporosis, indicating significant bone loss and a higher risk of fractures.
Because the number is negative, a lower T-score means weaker bones. The difference between -1.0 and -2.5 might not look dramatic on paper, but it represents a meaningful increase in fracture risk, particularly in the hip and spine.
Who Should Get Tested
The U.S. Preventive Services Task Force recommends routine bone density screening for all women 65 and older. Postmenopausal women younger than 65 should also be screened if they have risk factors such as low body weight, a parent who fractured a hip, smoking, or heavy alcohol use.
For men, there’s currently no universal screening recommendation. The evidence on the benefits of routine screening in men hasn’t been strong enough to establish a clear guideline, though doctors may still order the test for men with specific risk factors like long-term steroid use, low testosterone, or a history of fractures.
Central vs. Peripheral Scans
The standard DEXA scan described above is called a central scan because it measures the spine and hip. You may also encounter peripheral bone density tests at pharmacies, health fairs, or mobile screening events. These smaller, portable devices measure bone density in the wrist, heel, or finger.
Peripheral scans can give a general sense of bone health, but they’re not as accurate or comprehensive as a central DEXA scan. A peripheral result can’t be used to formally diagnose osteoporosis, and it won’t give your doctor the detailed information needed to track bone changes over time or make treatment decisions. If a peripheral scan suggests low bone density, you’ll typically be referred for a full central DEXA scan to confirm.