Bones Mineral Density (BMD) Test

There are different bone mineral density tests but the DEXA scan is most commonly used. Read more about bone density tests and how they may help to detect osteoporosis here.

What is Bone Mineral Densitometry?

Bone mineral densitometry is a test done to measure a person's bone mineral density (BMD). The measurements are used for the diagnosis of osteoporosis , estimation of the fracture risk and assessment of response to treatment.

There are three ways of checking your BMD, but the most commonly used method is DEXA.

Dual Energy X-ray Absorbitary (DEXA)

DEXA is a simple, low-radiation (about a quarter of a chest X-ray dosage) test that measures the mineral content of the bones.

A detector detects the energy emitted after an X-ray is passed through the patient. Bone mass will obstruct the energy passing through. Thus, the more energy emitted, the weaker the bone is.

The computer processes the data, tabulates the results and calculates the BMD value. Two scores are generated from this scan. One is the T-score, which indicates the amount of bone loss by comparing the patient's BMD at his/her current age to the peak bone mass achieved by young individuals. The other, the Z-score, retakes the patient's bone loss to his/her age-matched peers's expected bone loss to assess whether the patient's BMD is normal.

Why DEXA is Used (In Comparison With Other Methods of BMD)

DEXAUltrasound ​Quantitative CT Scan
  • ​Cheap. Short time scanning
  • ​Safe, no x-ray.
  • ​Very accurate as it can calculate at every level.
  • ​Not operator dependent so results can be compare across time.
  • ​Operator dependent. If the operator holds the probe differently, it can generate different values. Thus results are not comparable.
  • ​Time consuming.
  • ​Relatively safe, low dose of radiation
  • ​Not cost effective.

Osteoporosis and BMD

Osteoporosis is a condition where bones become thin and weak as bone tissue is lost faster than it can be replaced. It is diagnosed when the BMD measured falls below a critical threshold of 2.5 SD (standard deviation) from the average BMD of young healthy people.

Osteoporosis results in brittle bones. Bones in the wrist, spine and hip have the highest risk of breaking. As the condition is painless, people with osteoporosis are often unaware of their condition until their bone collapses or breaks. BMD is thus carried out as a predictive and preventive measure.

Who Should Do The Scan?

Osteoporosis has no symptoms. To detect osteoporosis before your bones fracture, you should have a BMD scan done, especially if you are in the high-risk group for osteoporosis.

Bone loss is a natural process for both men and women. However, women have a higher risk of getting osteoporosis. The following checklist should help you assess your risk; the more number of checks you have, the greater your risk of osteoporosis.

If you:
Have menopause or your ovaries have been removed (oestrogen level declines)
Are over 50 years old
Have lost height over the years
Are small-framed or have lighter, smaller bones 
Aare lactating (breastfeeding)
Seldom take milk or milk products (not enough calcium  in diet)
Are not physically active  and seldom exercise
Drink coffee, tea  or alcohol  regularly
Have family members with osteoporosis
Have fair skin

Preparation and Expectation

There are no special preparations required for BMD. You may eat and drink as usual and take your regular medicine when necessary.

On the day of your appointment, you will be asked to change into a hospital robe and your height and weight measurements will be taken. The radiographer will then assist you to lie down on the examination table.

Usually, the scan will be performed at your spine and hip. You will be required to remain still while the X-ray is being taken. For the spine examination, your legs will be propped up on a box to straighten the lumbar arch. Your feet will be aligned to a Perspex immobiliser for the hip examination so as to maintain the position of the hip. The whole procedure takes about 20 minutes to half an hour. You should not feel any discomfort during the examination. When it is done, a report will be generated and the findings either explained or sent to your referring doctor.

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