Bone density – a measure of bone health
Bones are pretty rigid; they form the skeletal system supporting various organs and motion.
Bones are also quite dynamic and are not some inert objects.
Bones play an essential role in the formation of blood cells and immunity.
The rigidity of bones is due to their high calcium and phosphorus content, which are present as hydroxyapatite.
In fact, these two minerals form 70% of the bone mass.
Mineralization and demineralization of bones is a regular process. In case of deficiency of these minerals, or other health issues, pathological bone demineralization may occur.
There are many reasons for bone demineralization.
But in adults, osteoporosis remains the primary cause.
Demineralization causes weakened bones and loss of bone density.
One should not confuse low bone density with low bone mass.
Low bone mass may be hereditary or due to low body weight.
In low bone mass, bones may be thin but still quite rigid-it is not essentially a pathology.
However, low bone density is a severe condition as it means low bone strength and a higher risk of fractures.
Fortunately, osteoporosis is reversible in most cases when diagnosed early enough.
Thus, early diagnosis of the condition is key to prevent complications or fractures. Bone Mineral Density (BMD) is the most reliable way to assess bone strength and severity of osteoporosis.
Decrease or increase of bone density is primarily recognized with the help of the BMD test.
This test is non-invasive and is quite like having an x-ray.
It is called a central dual-energy x-ray absorptiometry (or central DXA test). It can provide a lot of information about bone health, risk of fracture.
In addition, it can help assess the severity of osteoporosis and help know about the success of treatment.
Mostly, the test would be done on bones of arms and legs (peripheral bone density test), and if required, the test can also be done to assess the health of lumbar and hip joints.
BMD test cannot be regarded as highly accurate. Nonetheless, it provides a good assessment of bone health.
It compares the density of a person’s bones against well-established standards and then provides the score.
It is the most common scoring system for bone health.
It compares the bone density with the density of healthy young adults, and then the person receives T-score. If the score is “0,” it means that bone density is good and similar to a healthy adult.
The lower the bone T-score, the lower is the density. Scores between +1 to -1 are regarded as normal deviations.
A T-score of -1 to -2.5 indicates low bone mass, but it is still not osteoporosis. However, any score below that is a confirmed diagnosis of osteoporosis.
Normal Bone density is within 1 SD (+1 or −1) of the young adult mean.
Low bone mass Bone density is between 1 and 2.5 SD below the young adult mean (−1 to −2.5 SD).
Osteoporosis Bone density is 2.5 SD or more below the young adult mean (−2.5 SD or lower).
Severe (established) osteoporosis Bone density is more than 2.5 SD below the young adult mean, and there have been one or more osteoporotic fractures.
Table WHO osteoporosis diagnosis criteria based on T-score
High-risk individuals or those suspecting osteoporosis should go through a BMD test. Experts also recommend it as a screening test for adults older than 65 years of age.