What is a Bone Mineral Densitometry?
Bone mineral densitometry is a test used to measure a person’s bone mineral density (BMD), which is the amount of minerals, such as calcium, packed into a section of bone. The more minerals your bones contain, the denser and stronger they are likely to be. This quick and painless test can show whether your bones have become thin and fragile, often before you have had a fracture, so that you can take steps to protect them.
The measurements are used to:
- Diagnose osteoporosis, a condition in which bones become weak and brittle
- Estimate your risk of breaking a bone (a fracture)
- Assess how well you are responding to treatment for bone loss
Why Is Bone Density Testing Important?
Bone loss comes with age in both men and women. As bones lose density, they become fragile and can break easily, even from a minor fall, a bump or sometimes just bending or coughing. Osteoporosis is often called a “silent” condition because it usually causes no symptoms until a bone breaks.
Women are at a higher risk of osteoporosis than men. Oestrogen, a hormone that is essential for healthy bones, falls after menopause, and this leads to a rapid decrease in bone density in the years that follow.
Fractures from osteoporosis, especially hip and spine fractures, can cause long-term pain, loss of height, difficulty walking and loss of independence. A bone density test allows problems to be found and treated early, which can lower the risk of such fractures.
Why This Matters in Singapore
Singapore’s population is ageing rapidly, and with it, the number of people at risk of osteoporosis and fragility fractures is expected to rise. Hip fractures are a particular concern, because many people who break a hip need long periods of recovery and some do not regain their previous level of independence.
National clinical guidance in Singapore recommends that bone density testing should be considered for all postmenopausal women and men aged 65 and above, and for younger adults who have risk factors for bone loss. Doctors in Singapore may also use a simple tool, the Osteoporosis Self-Assessment Tool for Asians (OSTA), to help decide who should be sent for a scan.
Several everyday factors can affect bone health here. Many people spend most of their day indoors, which may mean lower vitamin D levels despite our sunny climate. Some Asian diets also contain less dairy, so calcium intake may fall short of what is recommended. And at home, slippery bathroom floors, loose mats and stairs can lead to falls, which are a leading cause of fractures in older adults.
Who Should Have a Bone Density Test?
Your doctor may recommend a bone density test if you:
- Are a woman who has gone through menopause, especially if menopause was early (at or before age 45)
- Are a man aged 65 or above
- Have broken a bone easily, for example from a minor fall, or have lost height or developed a stooped posture
- Have a family history of osteoporosis or fragility fractures, such as a parent who broke a hip
- Are on long-term medication that can weaken bones, such as steroid tablets
- Have a condition that can lower bone density, such as an overactive thyroid, low sex hormone levels or kidney, liver or inflammatory conditions
- Smoke, drink alcohol heavily, are underweight or are not very active
- Have had a history of falls or have been immobile for a long time
- Are already being treated for osteoporosis, and need to check how well treatment is working
Preparing for Your Bone Density Test
- Calcium tablets: Do not take calcium tablets, including multivitamins that contain calcium, for 24 hours before your test, as they may affect the results.
- Nuclear medicine scans: Please do not have a nuclear medicine scan within 48 hours before your test.
- Barium X-ray or CT scan: Do not have an X-ray examination with barium, or a CT scan with contrast, within the week before your appointment, as these can interfere with the scan. Tell us if you have had any of these recently, and we will advise you on rescheduling.
- Eating and drinking: You can eat a normal diet on the day of the test. No fasting is needed.
- What to wear: Wear comfortable, loose clothing without metal zips, buttons, buckles or hooks around the waist, as metal can affect the images. You may be asked to change into a gown. Leave jewellery and belts at home.
- Pregnancy: Tell our staff if you are pregnant or think you may be pregnant.
- Previous problems: Let us know if you have had spine or hip surgery, have metal implants, or have a curved spine (scoliosis), as these can affect the scan.
- What to bring: Your doctor’s referral letter, your NRIC (or passport if you are an international patient), any previous bone density reports for comparison, and a list of your medications.
What Happens During a Bone Density Test?
- You will be asked to lie down on your back on a flat, open X-ray table.
- For the spine scan, your legs are supported on a padded block so that your knees are bent and your lower back is flat. This straightens the curve in your lower spine and helps to give a clear image.
- For the hip scan, your feet are positioned and held inward, usually with a small brace, so that the hip bone is lined up correctly.
- A scanning arm passes slowly over your body. It does not touch you, and the machine is open, so it is not like being inside a tunnel.
- You will need to stay still while the X-rays are taken, and may be asked to hold your breath briefly.
What Happens After a Bone Density Test?
- You can return to your normal activities straight away, including eating and taking your usual medication. If you stopped taking calcium tablets for the test, ask your doctor when to restart.
- The images are reviewed by a doctor, and a report is prepared for your doctor.
- You will be given a follow-up appointment to review your test results.
Understanding Your Results
Your results are usually given as a “T-score”, which compares your bone density with that of a healthy young adult. In general:
- A T-score of -1.0 or higher is considered normal
- A T-score between -1.0 and -2.5 indicates low bone mass (sometimes called osteopenia). Your bones are thinner than normal but not yet in the osteoporosis range
- A T-score of -2.5 or lower indicates osteoporosis
For younger adults, such as premenopausal women and men under 50, a “Z-score” is often used instead, which compares your bone density with that of people of the same age, sex and body size.
Your doctor will look at your scan result together with your age, medical history, medications, previous fractures and other risk factors to estimate your overall chance of breaking a bone in the next ten years. A tool such as FRAX may be used to help with this. This helps to decide whether you need lifestyle changes, supplements, medication, or just monitoring.
If you are being treated for osteoporosis, your doctor may repeat the scan after one to two years to see how your bones are responding. For the most reliable comparison, it is best to have follow-up scans done on the same machine, so keep your previous reports.
Looking After Your Bones
Whatever your result, the following steps help to keep bones as strong as possible:
- Get enough calcium from foods such as dairy products, calcium-fortified soy milk, tofu, small fish eaten with the bones, and dark green leafy vegetables. Ask your doctor before taking calcium supplements
- Make sure you get enough vitamin D, from safe sun exposure, food and supplements if your doctor recommends them
- Do regular weight-bearing exercise, such as brisk walking, and muscle-strengthening and balance exercises. Activities such as tai chi can help to improve balance and reduce the risk of falls
- Do not smoke, and limit alcohol
- Make your home safer: keep walkways clear, use non-slip mats in the bathroom, make sure lighting is good and consider grab bars where needed
- Have your eyesight checked regularly, and ask your doctor to review any medicines that may cause dizziness
- Take any prescribed osteoporosis medication exactly as directed, and attend your follow-up appointments
