Osteoporosis is diagnosed primarily through a bone density scan called a DEXA scan, which measures how thick and strong your bones are. The results are reported as a number called a T-score: a score of -2.5 or lower indicates osteoporosis. But diagnosis often involves more than a single scan. Your doctor may also use blood tests, fracture risk calculators, and imaging to get the full picture of your bone health.
The DEXA Scan
A DEXA scan (dual-energy X-ray absorptiometry) is the gold standard for diagnosing osteoporosis. It works by passing two X-ray beams at different energy levels through your body, then measuring how much each beam is absorbed by your bones. Denser bone absorbs more energy, so the difference between the two beams reveals exactly how much mineral is packed into your skeleton.
The scan typically measures bone density at two sites: the hip and the spine. These are the areas most vulnerable to osteoporotic fractures and give the most clinically useful readings. The whole process takes about 10 to 15 minutes. You lie on a padded table while a scanning arm passes over you. There’s no injection, no enclosed space, and the radiation dose is extremely low.
One preparation detail worth knowing: you should stop taking calcium supplements 24 hours before the test. Undigested calcium in your system can interfere with the readings. You’ll also want to avoid wearing clothing with metal zippers or buttons near the scan area.
What Your T-Score Means
Your DEXA results come back as a T-score, which compares your bone density to that of a healthy 30-year-old adult at peak bone mass. The National Institute of Arthritis and Musculoskeletal and Skin Diseases breaks the ranges down like this:
- -1 or higher: Healthy bone density.
- -1 to -2.5: Osteopenia, a milder form of bone loss that isn’t yet osteoporosis but signals your bones are thinning.
- -2.5 or lower: Osteoporosis.
Each full point drop in your T-score represents a meaningful decrease in bone strength. Someone with a T-score of -3.0 has significantly more fragile bones than someone at -2.5, even though both fall in the osteoporosis range. Your doctor will look at the scores from both your hip and spine and typically base the diagnosis on whichever site shows the lowest value.
Z-Scores for Younger Adults
If you’re a premenopausal woman, a man under 50, or a child, your results may be reported as a Z-score instead. A Z-score compares your bone density to others of the same age and sex rather than to peak bone mass. A Z-score of -2.0 or lower is considered below the expected range and usually prompts your doctor to investigate underlying causes of bone loss rather than labeling it as typical osteoporosis.
Who Should Get Screened
The U.S. Preventive Services Task Force recommends routine bone density screening for all women aged 65 and older. For postmenopausal women younger than 65, screening is recommended if they have risk factors that increase fracture likelihood, such as a family history of hip fracture, low body weight, smoking, or long-term use of steroid medications.
For men, the evidence is less clear-cut. The Task Force hasn’t established a firm screening recommendation, but many clinicians will order a DEXA scan for men over 70 or for younger men with significant risk factors like long-term steroid use, heavy alcohol intake, or conditions that weaken bone.
The FRAX Fracture Risk Calculator
A T-score alone doesn’t always tell the whole story. Two people with the same bone density can have very different fracture risks depending on their age, health history, and lifestyle. That’s where the FRAX tool comes in. Developed by the World Health Organization, it calculates your 10-year probability of a major osteoporotic fracture.
FRAX factors in 10 variables: age, sex, body mass index, whether you’ve had a prior fragility fracture, whether a parent fractured a hip, current smoking status, steroid use, excess alcohol intake (typically three or more drinks per day), rheumatoid arthritis, and other causes of secondary osteoporosis. Bone density from a DEXA scan can be entered into the calculator but isn’t required, which makes FRAX useful even in settings where a scan isn’t available.
Your doctor may use your FRAX score to decide whether treatment is warranted, particularly if your T-score falls in the osteopenia range. Someone with osteopenia but a high FRAX score may benefit from medication, while someone with a similar T-score but few other risk factors may only need lifestyle changes and monitoring.
Physical Exam Clues
Before any scans or lab work, a physical exam can raise the first red flags. One of the most telling signs is height loss. People who have lost at least 1.5 inches (3.8 centimeters) from their tallest adult height may have compression fractures in their spine, and osteoporosis is one of the main causes. These fractures can happen gradually and without dramatic pain, so height measurement at every visit is a simple but important screening step.
A forward curvature of the upper back (sometimes called a dowager’s hump) is another visible indicator. Your doctor may also check for tenderness along the spine, which can suggest a recent vertebral fracture.
Vertebral Fracture Assessment
Many DEXA machines can perform a vertebral fracture assessment (VFA) during the same appointment as your bone density scan. This add-on captures a lateral image of your spine from roughly the mid-back down to the lower spine, looking for compression fractures that may not be causing symptoms.
VFA uses very low radiation and is far more convenient than a separate spine X-ray. It’s particularly useful if you have osteopenia or osteoporosis on your DEXA scan, significant height loss, or a history of back pain. Finding even one vertebral fracture changes the clinical picture considerably, because a prior fracture is one of the strongest predictors of future fractures. The sensitivity of VFA for detecting moderate to severe vertebral fractures is around 77%, with a specificity of about 80%, so it catches most significant fractures but may miss very mild ones.
Blood Tests to Rule Out Other Causes
If your DEXA scan shows low bone density, your doctor will often order blood work to check whether an underlying condition is driving the bone loss. This is especially important for younger patients or anyone whose bone loss seems disproportionate to their age and risk factors.
Common tests include calcium levels, which can reveal hyperparathyroidism (overactive parathyroid glands that pull calcium from bone) or other metabolic problems. Vitamin D levels are checked because a deficiency impairs your body’s ability to absorb calcium. Kidney function tests matter because the kidneys help regulate calcium and activate vitamin D. Thyroid hormone levels may be tested since an overactive thyroid accelerates bone breakdown. In some cases, doctors will also check for markers of conditions like celiac disease or multiple myeloma, a blood cancer that can weaken bones.
These tests don’t diagnose osteoporosis itself, but they determine whether your bone loss has a treatable underlying cause. Treating a vitamin D deficiency or an overactive thyroid, for example, can slow or partially reverse bone loss in ways that osteoporosis medication alone wouldn’t address.
Bone Turnover Markers
Once osteoporosis is diagnosed and treatment begins, your doctor may use blood tests called bone turnover markers to track how well your medication is working. These markers measure proteins released during the natural cycle of bone breakdown and rebuilding.
The most widely used marker is CTx (C-telopeptide), which reflects how actively your body is breaking down old bone. When anti-resorptive medications are working, CTx levels drop noticeably. Doctors can check these levels every three to six months to confirm you’re responding to treatment and taking your medication consistently, rather than waiting one to two years for a follow-up DEXA scan to show changes in density.
Bone turnover markers aren’t used to diagnose osteoporosis on their own, but research supports their value in predicting fracture risk and monitoring treatment. They fill the gap between DEXA scans and give your doctor earlier signals about whether your treatment plan needs adjusting.