Doctors use bone density testing to see how strong a person’s bones are. These tests can show if a person has low bone density and may be at risk of osteoporosis. There are a variety of methods to test a person’s bone density, including X-ray, CT, and ultrasound scans.

These different bone density tests can scan different types of bone in the body. In general, they measure the amount of bone material in a particular section of bone, such as the hips or spine.

The more bone material a person has in their bones, the higher their bone density will be.

Read on to learn about the different bone density tests, how they work, and when a doctor might use them.

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Adult humans have 206 bones. Bones are essential for allowing movement, protecting essential organs, and storing minerals. In order to do these jobs, bones have to be dense.

According to one 2020 article, around 90% of a person’s bone volume is made up of the extracellular matrix, which is the hard part of the bone. The extracellular matrix contains an inorganic bone matrix and an organic bone matrix.

Around 10% of a person’s bone volume is made up of bone cells. Bone cells produce and shape the extracellular matrix and regulate the passage of minerals in and out of the bone.

A person’s bones contain a large amount of their body’s minerals. The 2020 article states that this includes around 99% of a body’s storage of calcium, 85% of a body’s storage of phosphorus, and 40–60% of a body’s storage of magnesium and sodium.

Illnesses, medications, and increasing age can cause low bone density. When a person’s bone density lowers, they may be at greater risk of bone fractures or conditions such as osteoporosis.

There are several types of bone density test in clinical use. These include the following:

  • Dual energy X-ray absorptiometry (DXA): These tests are the most common. Doctors use DXA tests to determine the bone density of central bones, such as the hips or spine.
  • Peripheral DXA (pDXA): This test is another type of DXA test. A pDXA test measures the bone density of distal bones, such as the tibia (shin bone) and radius (a bone in the forearm).
  • Quantitative CT (QCT): This test measures the bone density of central bones using a CT scanner.
  • Peripheral QCT: This test measures the bone density of distal bones using a CT scanner.
  • Quantitative ultrasound (QUS): This type of test can show the bone density of certain distal bones, such as the tibia, radius, and calcaneus (heel bone). It does not use radiation to produce images.

All bone density tests work in similar ways. However, DXA and QCT tests both use X-rays to determine bone density, while QUS tests use ultrasound.

During a DXA or QCT scan, a doctor will use a machine that can emit and detect X-rays. A person’s bones will absorb different amounts of these X-rays depending on the mineral density of their bones.

By comparing the amount of X-ray radiation that the machine emits with the amount of X-ray radiation that the machine detects on the other side of a person’s body, a doctor can work out how much X-ray radiation the person’s bones absorbed.

The doctor can then use this number to estimate a person’s bone density.

QUS scans work in a similar way. However, instead of emitting and detecting X-rays, they work with ultrasound.

Ultrasound scans use high frequency sound waves. These sound waves echo as they come into contact with the bones and build up a picture of the inside of the body.

Unlike X-rays, ultrasound is not a form of radiation.

Some common uses for bone density tests are to detect bone fractures and conditions such as osteoporosis.

Osteoporosis is a condition that causes people to lose bone mass. According to one 2020 overview of the condition, osteoporosis affects around 70% of people over the age of 80 years.

Without treatment, osteoporosis can make people particularly vulnerable to bone fractures.

Many doctors recommend that older adults have regular bone density tests because osteoporosis is more common in later life.

The results of bone density tests are shown as a T-score. The T-score refers to the density of a person’s bones when compared with the average bone density of a young person of the same sex.

For example, a male with a T-score of -1 has a bone density that is 1 unit of measurement less than that of the average young male.

One 2016 study states that a T-score of -2.5 or under can indicate osteoporosis.

A person having a bone density test does not need to do anything to prepare. They will not need to fast, and they may not need to undress.

However, a person cannot wear any metallic piercings or accessories during a DXA or QCT scan, as metal can interfere with X-ray radiation.

Bone density scans do not take long, and they are generally over in around 2 minutes. During the scan, a person may have to lie down on a table with their legs raised by a box.

People rarely receive the results of the test straight away. This is because a trained doctor has to interpret the results first.

Scientists know that different bone density tests have various benefits and limitations.

For example, although DXA scans can reliably detect a person’s risk of bone fractures, they may be less effective for people with obesity and those who have previously fractured bones.

QCT scans can give very precise measurements of different parts of the bone structures. However, they are less standardized than DXA tests. This can make it difficult to compare the results of different QCT scans.

QUS scans are helpful because the machinery is portable and does not produce any harmful radiation. However, QUS scans may be less reliable and accurate than DXA or QCT scans.

It is not always possible for a person to improve their bone density. However, the 2020 overview of osteoporosis notes that, in many cases, making certain lifestyle changes can help improve bone density.

These lifestyle changes include:

  • quitting smoking, if applicable
  • avoiding alcohol
  • eating a calcium-rich diet
  • taking vitamin D supplements
  • exercising regularly

There are also a wide range of medications that can help people with bone density conditions such as osteoporosis.

Having good bone density is important for overall health. Low bone density can be a sign of conditions such as osteoporosis, and it may put a person at risk of bone fractures.

Scientists have developed a wide variety of bone density testing methods. These can help doctors detect low bone density before it becomes severe or detect osteoporosis so that a person can begin treatment.

X-ray scans, CT scans, and ultrasound scans can measure a person’s bone density. Doctors use DXA scans most widely.

There are benefits and limitations to each of the different bone density tests. For instance, X-ray and CT scans use radiation, but ultrasound scans may not be as accurate.

As a person ages, they may need to go for more frequent bone density tests to make sure that their bones are healthy.

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