Bone Density Screening: Who Needs a DXA Scan and What a T-Score Means

Bone density screening is a short, painless scan called a DXA that measures how strong your bones are and reports it as a single number, the T-score, used to flag people at higher risk of breaking a bone before any break happens. Like blood pressure, falling bone density gives no warning signs, so the only way to catch it early is to measure it.

The first time I went for one I expected something like an MRI, a tunnel and a long wait. Instead I lay on an open table in my own clothes while a flat arm slid quietly over my hip, and it was finished before I had settled into worrying about it. The hard part was not the scan. It was understanding the printout afterwards.

What a DXA scan is and how it works

A DXA scan (also written DEXA, for dual-energy X-ray absorptiometry) is the standard test for measuring bone mineral density.¹ It passes two low-energy X-ray beams through the body, usually at the hip and lower spine, and from the difference in how the beams are absorbed it calculates how much mineral is packed into the bone. Those two sites are chosen because they are where fragility fractures do the most damage.

The practical experience is undramatic. You lie still on a padded table, a scanning arm moves above you, and nothing touches or enters the body. It takes roughly 10 to 20 minutes and the radiation dose is very low, a small fraction of a routine chest X-ray. Because it is quick and low-dose, it suits its job as a screening tool for people with no symptoms, which is the whole point of screening rather than waiting for a problem to announce itself.

Reading the result: what a T-score means

The DXA result that matters most for screening is the T-score, which compares your bone density to that of a healthy young adult of the same sex. The World Health Organization sets the cut-offs that almost every country uses: a T-score of −1.0 or above is normal, between −1.0 and −2.5 is low bone mass (often called osteopenia), and −2.5 or below meets the definition of osteoporosis.² Each whole step down on this scale represents a meaningful drop in bone strength.

A second number, the Z-score, sometimes appears alongside it. The Z-score compares you to others of your own age and sex rather than to a young adult, and it is used mainly in younger people, where an unexpectedly low value can prompt a look for a specific underlying cause. For routine screening in older adults, the T-score is the figure that drives the conversation. As with any screen, a low number is a flag for assessment, not a diagnosis of fracture, in the same way an abnormal test is the start of a conversation, not the end.

Who is screened, and when

Bone density screening is targeted by risk rather than offered to everyone. The most consistent recommendation across guideline bodies is to screen women from around age 65, the age at which fracture risk in the general female population rises enough to make routine testing worthwhile.¹ Earlier screening is offered to younger postmenopausal women, and to men, when specific risk factors are present.

Those risk factors include a previous fragility fracture (a break from a fall at standing height or less), long-term oral steroid use, low body weight, smoking, heavy alcohol intake, early menopause, and a parental history of hip fracture. The reason this matters is scale: osteoporosis is common and largely silent, and one widely cited estimate is that worldwide roughly 1 in 3 women and 1 in 5 men over the age of 50 will experience an osteoporotic fracture in their remaining lifetime.³ There is no single global start age, so the honest answer to “when should I have this” is that it depends on your age, sex, and risk profile, decided with a clinician.

The T-score is not the whole story

A common misunderstanding is that the T-score alone decides everything. It does not. Bone density is one input into fracture risk, and two people with the same T-score can have very different chances of breaking a bone depending on their age, whether they have fractured before, and other factors. This is why clinicians increasingly combine the DXA result with a structured fracture-risk estimate.

A widely used example is FRAX, a tool that takes the femoral-neck bone density together with age, sex, weight, and clinical risk factors to estimate the 10-year probability of a major fracture.⁴ That estimate, rather than the T-score in isolation, is what guides whether to recommend lifestyle measures, treatment, or simply a recheck later. It mirrors the risk-based logic that runs through sensible prevention generally, the same approach used in building a screening plan around your own risk rather than testing maximally.

What happens after the scan

A normal result usually means a recheck in several years, with attention to the modifiable factors that protect bone: weight-bearing and resistance exercise, adequate calcium and vitamin D, not smoking, and moderating alcohol. A result in the low-bone-mass range is a prompt to address those factors and to reassess overall fracture risk, not an automatic prescription. A result in the osteoporosis range, or a high calculated fracture risk, opens a conversation about treatment to reduce the chance of a future break.

Repeat intervals are set by risk rather than a fixed calendar. The principle is the same one that should guide any screening decision: match the frequency of testing to the individual’s risk, and decide it with someone who knows their history. A single number on a printout is the beginning of that decision, not the end of it.

This article is general information, not medical advice. For your own scan, T-score, and any treatment, see a qualified clinician who knows your history.