Osteoporosis is diagnosed primarily through a bone density scan called a DXA (dual-energy X-ray absorptiometry), which measures how dense your bones are and produces a score that falls into one of three categories: normal, low bone density, or osteoporosis. The scan is painless, takes about 10 to 20 minutes, and uses very low levels of radiation. In some cases, additional imaging or blood tests are needed to get the full picture.
The DXA Scan: The Standard Diagnostic Test
A DXA scan is the gold standard for diagnosing osteoporosis. The machine sends two low-dose X-ray beams through your bones and measures how much energy each beam absorbs, which reveals how much mineral (mainly calcium) is packed into a given area of bone. The result is your bone mineral density, or BMD.
Most DXA scans focus on the lower spine and hips because these are the sites most prone to osteoporotic fractures and where measurements are most reliable. These central DXA devices are better standardized and more sensitive than portable devices that scan your wrist or heel. Peripheral scans at the wrist or heel can flag low bone mass as a screening tool, but they aren’t accurate enough to track how you respond to treatment. If a peripheral scan suggests you need medication, you’ll be sent for a full central DXA before starting.
Understanding Your T-Score
Your DXA results come back as a T-score, which compares your bone density to that of a healthy 30-year-old adult of the same sex (the age when bones are at their peak strength). The World Health Organization classifies bone density into three ranges:
- 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.
- T-score of -2.5 or lower: Osteoporosis.
A T-score of -2.5 or below combined with a history of a fracture from minor trauma (like a fall from standing height) is classified as severe osteoporosis. The further below -2.5 your score falls, the greater your fracture risk.
For younger adults, children, and premenopausal women, doctors use a Z-score instead. This compares your bone density to other people of the same age and sex rather than to a 30-year-old. A very low Z-score suggests something beyond normal aging is weakening your bones and usually triggers a search for underlying causes.
Who Should Get Screened
The U.S. Preventive Services Task Force recommends bone density screening for all women aged 65 and older. Postmenopausal women younger than 65 should also be screened if they have risk factors that raise their chances of a fracture, such as low body weight, a parent who broke a hip, smoking, or excessive alcohol use. These recommendations apply to adults without a known history of fragility fractures or conditions already linked to bone loss.
For men, there is no universal screening recommendation. The evidence on whether routine screening prevents fractures in men hasn’t been established clearly enough for a blanket guideline. That said, many doctors will order a DXA for men over 70 or for younger men with specific risk factors like long-term steroid use, low testosterone, or a history of fractures.
When Spinal Imaging Is Added
A standard DXA measures density but doesn’t always catch vertebral compression fractures, which are the most common osteoporotic fractures and often go unnoticed. Many people with spinal fractures never feel a sudden “break.” Instead, the vertebrae gradually collapse, leading to height loss, a rounded upper back, or chronic back pain that gets attributed to aging.
A Vertebral Fracture Assessment (VFA) is a low-dose X-ray image of the spine that can be done during the same DXA appointment. Your doctor may add this if you’re a postmenopausal woman aged 70 or older, if you’ve lost more than 4 cm (about 1.5 inches) of height over your lifetime, if you have a visible curve in your upper back, or if you’ve been on long-term glucocorticoid therapy. For men, the thresholds are slightly different: VFA is typically considered at age 80 or older, or with historical height loss greater than 6 cm.
Documenting whether a vertebral fracture already exists can change the course of treatment. A person with both low bone density and an existing spinal fracture may be started on a stronger class of medication than someone with low density alone.
QCT: An Alternative to DXA
Quantitative computed tomography (QCT) is another way to measure bone density, though it’s used less often. Unlike DXA, which gives a flat, two-dimensional measurement, QCT produces a three-dimensional image and measures the density of the inner spongy bone (trabecular bone) separately. This inner bone is more metabolically active and loses density faster, so QCT can sometimes detect osteoporosis that a DXA misses.
A large meta-analysis found that QCT identified nearly five times as many osteoporosis cases as DXA in the same group of patients. The difference was especially pronounced in men, where QCT caught roughly eight times more cases, and in people over 65, where it caught about six times more. QCT uses different thresholds than DXA: a trabecular bone density at or below 80 mg/cm³ indicates osteoporosis, while values between 80 and 120 mg/cm³ indicate osteopenia.
QCT isn’t the first choice for routine screening because it delivers more radiation than DXA and costs more. But it’s increasingly used “opportunistically,” meaning if you’ve already had an abdominal or chest CT scan for another reason, that same scan data can be analyzed to estimate your bone density without any extra radiation exposure.
Blood Tests to Rule Out Other Causes
A DXA scan tells you that bone density is low, but it doesn’t explain why. In many cases, the cause is straightforward: aging and hormonal changes after menopause. But sometimes low bone density is driven by an underlying condition, and treating the bone loss without addressing the root cause won’t work well.
Doctors commonly order a panel of blood and sometimes urine tests alongside or after a DXA to check for secondary causes of bone loss. These typically include:
- Vitamin D levels: Low vitamin D impairs calcium absorption and is one of the most common and correctable contributors to bone loss.
- Calcium levels in blood and urine: Abnormal calcium can point to problems with the parathyroid glands or kidneys.
- Thyroid function: An overactive thyroid accelerates bone breakdown.
- Parathyroid hormone (PTH): Elevated PTH pulls calcium out of bones to maintain blood calcium levels.
Depending on your age, sex, and medical history, additional tests may be ordered to check for conditions like celiac disease, multiple myeloma, or hormonal imbalances that quietly erode bone.
Bone Turnover Markers
You may also hear about blood tests that measure how quickly your body is building and breaking down bone. These “bone turnover markers” include one that reflects bone formation (P1NP) and one that reflects bone breakdown (CTx). Both are endorsed by international osteoporosis organizations as reference markers.
These markers are not used to diagnose osteoporosis. Their main role is monitoring treatment. A typical protocol involves drawing blood before starting medication to establish a baseline, then repeating the test about three months later. If the markers shift in the right direction by a meaningful amount, it’s a sign the medication is working. If they don’t change, it may indicate the medication isn’t effective or isn’t being taken consistently. This provides much faster feedback than waiting one to two years for a follow-up DXA to show a change in bone density.
Diagnosis Without a DXA
In some cases, osteoporosis is diagnosed clinically without a bone density test. If you break a bone from a low-impact event, like falling from standing height or less, that fracture alone can be enough for a diagnosis, particularly if it involves the hip, spine, or wrist. These “fragility fractures” are a hallmark of osteoporosis regardless of what a DXA score might show. In fact, some people fracture bones while their T-score is still technically in the osteopenia range, which is why fracture risk assessment tools that factor in age, weight, smoking, and family history are sometimes used alongside or instead of DXA results to guide treatment decisions.