Bone densitometry

BONE MINERAL DENSITY (BMD) TEST

Diagnosis

In consultation with a doctor, osteoporotic fractures can be prevented. Your doctor will take a thorough medical history that includes information on any recent fractures and may determine the next step is to have a bone mineral density (BMD) test.

What is a Bone Mineral Density (BMD) test?

Traditional X-rays can’t measure bone density, but they can identify spine fractures. Bone mineral density (BMD) has to be measured by more specialised techniques. A number of different types of BMD tests are available, but the most commonly used is DXA (dual-energy X-ray absorptiometry)

DXA is a low radiation X-ray capable of detecting quite small percentages of bone loss. It is used to measure spine and hip bone density, and can also measure bone density of the whole skeleton. There are a number of different types of test options [1]:

  • DXA (peripheral DXA) measures bone mass at the forearm, finger and heel
  • SXA (single-energy X-ray absorptiometry) measures the heel or wrist
  • DPA (dual photon absorptiometry) measures the spine, hip or total body
  • SPA (single photon absorptiometry) measures the wrist
  • QCT (Quantitative Computed Tomography) measures the spine or hip
  • PQCT (peripheral QCT) measures the forearm
  • QUS (Quantitative Ultrasound) uses sound waves to measure the heel or finger

A DXA scan, which is used to measure spine and hip bone density, is the most common technique for assessing the risk of osteoporosis.

bmd

What do my test results mean?

The World Health Organization has defined a number of threshold values (measurements) for osteoporosis. The reference measurement is derived from bone density measurements in a population of healthy young adults (called a T-score). Osteoporosis is diagnosed when a person’s BMD is equal to or more than 2.5 standard deviations below this reference measurement [2].

Osteopenia is diagnosed when the measurement is between 1 and 2.5 standard deviations below the young adult reference measurement.

StatusHip BMD
NormalT-score of -1 or above
OsteopeniaT-score lower than -1 and greater than -2.5
OsteoporosisT-score of -2.5 or lower
Severe osteoporosisT-score of -2.5 or lower, and presence of at least one fragility fracture

If the results of your BMD test show osteopenia or osteoporosis, it does not automatically mean that you will have a fracture. There are lifestyle changes and a number of available therapies that your doctor might prescribe to slow down bone loss and help prevent fractures.

There are a number of other methods for diagnosing osteoporosis that have been used extensively in clinical trials and epidemiological studies. These include radiological assessments and Bone Turnover Markers (BTM). Read more information on these methods of diagnosis.

Radiological assessment of vertebral fracture

Back pain and loss of height can be the first symptoms of vertebral fractures induced by osteoporosis. In order to assess the severity of vertebral fractures, a semi-quantitative method based on visual inspection has been developed. It has been extensively used in clinical trials and epidemiological studies. The severity of the fracture is assessed by measuring the extent of vertebral height reduction, by its morphological changes, and by differentiating the fracture from nonfracture deformities .

Grades are assigned to each vertebra based on the degree of height reduction.

This method does not link the type of deformity with the grading of the fracture. One advantage of this method is by assessing the severity of the deformation, new deformities occurring on a prevalent vertebral fracture can be assessed within the range of grading.

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Vertebral Fractures Semi-Quantitative Grading
Genant H. et al J Bone Miner Res. 1993; 8:1137-42

Quantitative methods such as morphometry or magnetic resonance imaging (MRI) have been developed over the past years and can be used to assess more precisely the features of vertebral fractures.

Bone Turnover Markers (BTM)

Bone Turnover Markers (BTM) have been extensively used in clinical research to monitor the efficacy and mechanisms of action of new drugs. There are three categories of BTM depending on their origination from the bone mineral unit (BMU): bone resorption markers, bone formation markers and markers of osteoclast regulatory proteins.

These markers, measured in serum or urine, are not disease-specific. They assess alterations in skeletal metabolism, regardless of the underlying cause.

Combining BMD with BTM could improve fracture prediction in postmenopausal women. One advantage of biochemical markers compared to BMD is early estimation of treatment effect.

Significant changes in BTM can be seen during anti-resorptive therapy after a few weeks of treatment; whereas individual monitoring with DXA usually requires 1-2 years to identify significant changes. As adherence is an important issue of long-term therapy in chronic disease, it has been suggested that BTM could be used in clinical practice to assess the patient’s adherence to treatment and also provide feedback on the effectiveness of the medication