3 days ago
What is bone mineral density, and how is it tested?
When Debra cracked both a tooth and a bone in her foot in the same year, she thought something was not right.
But it wasn't until she sought help from her doctor for brain fog and tiredness due to perimenopause that the topic of bone health came up.
After finding out Debra's mother and father had osteoporotic fractures, the doctor sent her off to get a specialised X-ray called a bone density scan.
That was how Debra, 45, discovered she had osteopenia, a condition marked by low bone density, which could have been linked to her fractures.
A decrease in bone density becomes more common as you age.
This can make your bones weaker and increase the risk of "fragility fractures", which happen after relatively minimal trauma.
Activities such as sneezing, turning in bed or even hugging a grandchild can cause a fracture.
In Debra's case, she cracked her tooth in her sleep, and she fractured her toe slipping in the wet in her trainers.
Because conditions of low bone density such as osteopenia and osteoporosis can have no obvious symptoms, they're often not diagnosed until after a person breaks a bone.
But there are ways to assess bone density and strength, and determine a person's risk of fragility fractures.
If a test shows you have low bone density, preventing further loss or building bone density may help reduce the risk of fractures.
So what is a bone density test, who is eligible to get one, and what can they tell us about our bones?
Healthy Bones Australia recommends women and men over 50 should have a scan if they have osteoporosis risk factors, although younger adults like Debra with risk factors may also benefit from one.
Risk factors include:
Some medications including corticosteroids used for asthma or those that treat cancers by blocking hormones can also lead to bone loss.
Smoking, excessive alcohol and a sedentary lifestyle also increase your risk.
Given the sharp drop in bone density that can occur post menopause, bone health expert Shoshana Sztal-Mazer of Alfred Health in Melbourne advises all women get a scan after menopause.
"It would be justified for anybody over 50 to have a [bone density scan], especially women over 50, then you know what your baseline is and what your drop is later on."
Healthy Bones Australia provides a survey that can help you assess your risk factors for osteoporosis and produces a report you can discuss with your doctor.
Some people qualify for Medicare reimbursement.
You need a referral from a GP to get a bone scan, which are performed by radiology companies, public hospitals and some specialists.
A scan costs around $80 to $120, CEO of Healthy Bones Australia Greg Lyubomirsky says.
People over 70, and anyone diagnosed with, or at risk of, osteoporosis can get a rebate.
You may also be able to get a rebate regardless of your age if you've already had a fracture, so talk to your doctor to see if you're eligible.
However, there are some inconsistencies, with post-menopausal women taking oestrogen-blocking treatments for breast cancer unable to claim a rebate, while men taking testosterone-blocking treatments for prostate cancer can.
Mr Lyubomirsky says his organisation is calling for this inconsistency to be changed, as well as decreasing the automatic age limit for rebates to 65 to help reduce the burden of fractures.
The standard test for bone density is a dual energy X-ray absorptiometry (DEXA or DXA) scan, which uses X-rays to measure minerals such as calcium in the skeleton.
The scan, which takes around 15 minutes, usually focuses on the hip and spine because this is where fractures are most likely to occur.
The more minerals present in those sites, the higher your bone mineral density, and the stronger your bones are likely to be.
A DEXA scan provides a bone mineral density measurement in grams per cubic centimetre.
The key number though, for people over 50, is what's called a "T score", which compares your bone mineral density to that of a young person's bones (which are designated as having a score of 0).
For every point that drops below 0, the risk of fracture increases by 1.5 to 2 times.
A T score of -2.5 or lower will give you a diagnosis of osteoporosis, which is regarded as the highest risk fracture.
In this case, doctors will commonly prescribe drugs to help counter the lost bone mineral density, along with adequate calcium and vitamin D and appropriate exercise. They will also recommend follow-up DEXA scans.
If you get a T score of -1 to -2.5, you will be diagnosed with osteopenia, like Debra. This means your bone density is low but not so low that you qualify for an osteoporosis diagnosis.
A second number, called a "Z score", gives an indication of your bone mineral density compared to the average for your age group, ethnicity, and sex.
It is generally used for younger people, but can be useful in older people as it may point to other reasons for loss of bone mineral density beyond the age-related decline.
How low your bone mineral density is, your age and other risk factors will then help determine the course of action your GP and other qualified health professionals recommend.
Debra, for example, was prescribed hormone replacement therapy by her GP to help her perimenopause symptoms and her bones, and she was advised to take vitamin D and calcium supplements.
A female health specialist also mentioned the benefit of certain exercises, so now she either runs or goes to the gym most days.
Your GP can also refer you to a physiotherapist or exercise physiologist to create a tailored exercise program, with up to five visits a year subsidised by Medicare if you have a team care arrangement in place.
DEXA scans have some limitations since most fragility fractures occur in people who haven't been diagnosed with osteoporosis, as defined by a bone density test.
"If you use bone mineral density, you'll only pick up about 20 to 30 per cent of the people who break bones," Austin Health endocrinologist and bone biologist Ego Seeman says.
In addition to having a DEXA scan, your doctor can use calculation tools to help assess your risk of fracture.
Meanwhile, Professor Seeman, who says he pioneered the use of DEXA machines in Australia, is also using detailed three-dimensional "micro-architecture" of bones to study why people with osteopenia get fractures.
"Their architecture has decayed, but it's not captured by the bone density machine," he says.
This technique is essentially still only used in research, but Professor Seeman, who is a medical director of a company building a scanning machine, says a recent study he co-authored provided some promising findings.
"The bone mineral density machine picks up 30 per cent of the fractures that occur over eight years, whereas when you add the micro-architecture, it picks up 70 per cent."
Dr Sztal-Mazer, who is also currently studying how bone micro-architecture is related to fractures, says the "Holy Grail" for researchers is reducing fragility fractures by finding better ways to measure our risk.
She describes bone density and bone micro-architecture as different "surrogates" for this.
"We're just trying desperately trying to find the right surrogate for assessing our risk of fracture."
