DEXA Bone Density Scan: What Your T-Score and Z-Score Mean

Osteoporosis is often called a silent disease, because bones can thin for years without any symptoms. A DEXA scan measures bone strength before a fracture happens, and your T-score is the key number.

Imagine your mother breaking her wrist after a simple trip on the pavement. Her healthcare provider orders a DEXA scan, and the report says “T-score -2.8, osteoporosis”. She had no idea her bones were fragile.

What a DEXA scan is

DEXA (or DXA) stands for dual-energy X-ray absorptiometry. It uses very low-dose X-rays to measure the mineral density of your bones, usually at the hip and lower spine, and sometimes the forearm.,It is the standard test for diagnosing osteoporosis and estimating your risk of fractures. The radiation dose is very small, lower than a standard chest X-ray.

Who might need a scan

• Women after the menopause with risk factors for osteoporosis
• Anyone who has had a fracture from a minor fall
• People taking long-term steroid tablets
• People with conditions that affect bones, such as rheumatoid arthritis, coeliac disease, an overactive thyroid or early menopause
• Those with low body weight, heavy drinking or smoking
• Some men, especially over 70 or with risk factors

What happens on the day

You can usually eat and drink normally. You may be asked to avoid calcium supplements for 24 hours before. Wear comfortable clothes without metal zips, buttons or buckles near the hips or waist, or you may be asked to change into a gown.,You lie on your back on a padded table while a scanner arm passes slowly over your body. You need to keep still for a few minutes. The scan is painless and usually takes 10 to 20 minutes.

Understanding T-scores

The T-score compares your bone density with that of a healthy young adult of the same sex. It is reported as the number of standard deviations above or below that average.,The World Health Organization categories are: a T-score of -1.0 or above is normal; between -1.0 and -2.5 is low bone density, often called osteopenia; and -2.5 or below is osteoporosis. A T-score of -2.5 or lower with a fragility fracture is sometimes described as severe osteoporosis.

What is a Z-score?

The Z-score compares your bone density with people of your own age, sex and size. It is mainly used for children, premenopausal women and younger men. A Z-score of -2.0 or lower suggests bone density is lower than expected for your age and may prompt a search for an underlying cause.

Fracture risk is more than the T-score

Healthcare providers often combine your bone density with other risk factors using a tool such as FRAX. This estimates your chance of a major osteoporotic fracture or hip fracture over the next 10 years.,Two people with the same T-score can have very different fracture risks, depending on age, previous fractures, steroid use, family history and other factors. Treatment decisions are usually based on overall risk.

Treatment options

• Bisphosphonates, such as alendronic acid, taken weekly as tablets, or zoledronic acid given yearly as a drip
• Denosumab injections every six months
• Bone-building treatments such as teriparatide for people at very high risk
• Hormone replacement therapy for some women around the menopause
• Calcium and vitamin D supplements if intake is low

Protecting your bones

• Do weight-bearing and muscle-strengthening exercise, such as walking, dancing and resistance training
• Get enough calcium from foods such as dairy, fortified plant milks, tinned fish with bones and leafy greens
• Make sure you get enough vitamin D, especially in winter
• Stop smoking and limit alcohol
• Reduce falls risk: remove trip hazards, check eyesight and ask about balance exercises

Who is most at risk of osteoporosis

Bone density peaks in early adulthood and slowly falls with age. Women lose bone more quickly in the years after the menopause because of falling oestrogen levels, which is why osteoporosis is much more common in women. However, men are affected too, and men who have a hip fracture are more likely than women to have serious complications.

Other risk factors include a parent who had a hip fracture, low body weight, smoking, drinking more than recommended amounts of alcohol, long-term steroid tablets, rheumatoid arthritis, eating disorders, early menopause and some hormone-blocking treatments for breast or prostate cancer.

Bisphosphonate tips

• Take alendronic acid first thing in the morning on an empty stomach with a full glass of plain water
• Stay upright and wait at least 30 minutes before eating, drinking anything else or taking other medicines
• Tell your dentist you take a bisphosphonate before any dental extraction
• Report new thigh or groin pain, which is a rare side effect
• Do not stop treatment without discussing it with your healthcare provider

Falls prevention matters too

Most fractures happen after a fall. Strengthening and balance exercises, such as tai chi or programmes run by physiotherapists, reduce falls. At home, good lighting, removing loose rugs, using grab rails and wearing well-fitting shoes all help. Ask for a medicines review if any of your medicines make you dizzy or drowsy.

Frequently asked questions

How often should DEXA be repeated?

Often every two to five years, depending on your results and treatment.

Can osteopenia turn into osteoporosis?

It can, which is why lifestyle measures and follow-up matter.

Does osteoporosis cause pain?

Not on its own. Pain usually comes from fractures, such as spinal fractures, which can cause back pain and height loss.

But I feel fine. Why treat bone density?

The aim is to prevent a fracture, especially a hip fracture, which can seriously affect independence and health in older adults.

Related: Osteoporosis risk and prevention · Vitamin D deficiency

Sources: World Health Organization, Royal Osteoporosis Society, International Osteoporosis Foundation, Bone Health and Osteoporosis Foundation (US), National Institute for Health and Care Excellence.